diff --git a/merkle/iavl.go b/merkle/iavl.go
index 000326b8d..6b6ebde46 100644
--- a/merkle/iavl.go
+++ b/merkle/iavl.go
@@ -30,11 +30,11 @@ func (self *IAVLTree) Height() uint8 {
 }
 
 func (self *IAVLTree) Has(key Key) bool {
-    return self.root.Has(key)
+    return self.root.Has(nil, key)
 }
 
 func (self *IAVLTree) Put(key Key, value Value) (err error) {
-    self.root, _ = self.root.Put(key, value)
+    self.root, _ = self.root.Put(nil, key, value)
     return nil
 }
 
@@ -43,11 +43,11 @@ func (self *IAVLTree) Hash() ([]byte, uint64) {
 }
 
 func (self *IAVLTree) Get(key Key) (value Value, err error) {
-    return self.root.Get(key)
+    return self.root.Get(nil, key)
 }
 
 func (self *IAVLTree) Remove(key Key) (value Value, err error) {
-    new_root, value, err := self.root.Remove(key)
+    new_root, value, err := self.root.Remove(nil, key)
     if err != nil {
         return nil, err
     }
@@ -94,13 +94,23 @@ func (self *IAVLNode) Value() Value {
     return self.value
 }
 
-func (self *IAVLNode) Left() Node {
+func (self *IAVLNode) Left(db Db) Node {
     if self.left == nil { return nil }
-    return self.left
+    return self.left_filled(db)
 }
 
-func (self *IAVLNode) Right() Node {
+func (self *IAVLNode) Right(db Db) Node {
     if self.right == nil { return nil }
+    return self.right_filled(db)
+}
+
+func (self *IAVLNode) left_filled(db Db) *IAVLNode {
+    // XXX
+    return self.left
+}
+
+func (self *IAVLNode) right_filled(db Db) *IAVLNode {
+    // XXX
     return self.right
 }
 
@@ -111,29 +121,29 @@ func (self *IAVLNode) Size() uint64 {
     return self.size
 }
 
-func (self *IAVLNode) Has(key Key) (has bool) {
+func (self *IAVLNode) Has(db Db, key Key) (has bool) {
     if self == nil {
         return false
     }
     if self.key.Equals(key) {
         return true
     } else if key.Less(self.key) {
-        return self.left.Has(key)
+        return self.left_filled(db).Has(db, key)
     } else {
-        return self.right.Has(key)
+        return self.right_filled(db).Has(db, key)
     }
 }
 
-func (self *IAVLNode) Get(key Key) (value Value, err error) {
+func (self *IAVLNode) Get(db Db, key Key) (value Value, err error) {
     if self == nil {
         return nil, NotFound(key)
     }
     if self.key.Equals(key) {
         return self.value, nil
     } else if key.Less(self.key) {
-        return self.left.Get(key)
+        return self.left_filled(db).Get(db, key)
     } else {
-        return self.right.Get(key)
+        return self.right_filled(db).Get(db, key)
     }
 }
 
@@ -176,6 +186,10 @@ func (self *IAVLNode) WriteTo(writer io.Writer) (written int64, hashCount uint64
     if self.right != nil { nodeDesc |= 0x04 }
     write([]byte{nodeDesc})
 
+    // node height & size
+    write(UInt8(self.height).Bytes())
+    write(UInt64(self.size).Bytes())
+
     // node key
     keyBytes := self.key.Bytes()
     if len(keyBytes) > 255 { panic("key is too long") }
@@ -209,7 +223,7 @@ func (self *IAVLNode) WriteTo(writer io.Writer) (written int64, hashCount uint64
 
 // Returns a new tree (unless node is the root) & a copy of the popped node.
 // Can only pop nodes that have one or no children.
-func (self *IAVLNode) pop_node(node *IAVLNode) (new_self, new_node *IAVLNode) {
+func (self *IAVLNode) pop_node(db Db, node *IAVLNode) (new_self, new_node *IAVLNode) {
     if self == nil {
         panic("self can't be nil")
     } else if node == nil {
@@ -222,96 +236,96 @@ func (self *IAVLNode) pop_node(node *IAVLNode) (new_self, new_node *IAVLNode) {
 
         var n *IAVLNode
         if node.left != nil {
-            n = node.left
+            n = node.left_filled(db)
         } else if node.right != nil {
-            n = node.right
+            n = node.right_filled(db)
         } else {
             n = nil
         }
         node = node.Copy()
         node.left = nil
         node.right = nil
-        node.calc_height_and_size()
+        node.calc_height_and_size(db)
         return n, node
 
     } else {
 
         self = self.Copy()
         if node.key.Less(self.key) {
-            self.left, node = self.left.pop_node(node)
+            self.left, node = self.left_filled(db).pop_node(db, node)
         } else {
-            self.right, node = self.right.pop_node(node)
+            self.right, node = self.right_filled(db).pop_node(db, node)
         }
-        self.calc_height_and_size()
+        self.calc_height_and_size(db)
         return self, node
 
     }
 }
 
-func (self *IAVLNode) rotate_right() *IAVLNode {
+func (self *IAVLNode) rotate_right(db Db) *IAVLNode {
     self = self.Copy()
-    sl :=  self.left.Copy()
+    sl :=  self.left_filled(db).Copy()
     slr := sl.right
 
     sl.right = self
     self.left = slr
 
-    self.calc_height_and_size()
-    sl.calc_height_and_size()
+    self.calc_height_and_size(db)
+    sl.calc_height_and_size(db)
 
     return sl
 }
 
-func (self *IAVLNode) rotate_left() *IAVLNode {
+func (self *IAVLNode) rotate_left(db Db) *IAVLNode {
     self = self.Copy()
-    sr :=  self.right.Copy()
+    sr :=  self.right_filled(db).Copy()
     srl := sr.left
 
     sr.left = self
     self.right = srl
 
-    self.calc_height_and_size()
-    sr.calc_height_and_size()
+    self.calc_height_and_size(db)
+    sr.calc_height_and_size(db)
 
     return sr
 }
 
-func (self *IAVLNode) calc_height_and_size() {
-    self.height = maxUint8(self.left.Height(), self.right.Height()) + 1
-    self.size = self.left.Size() + self.right.Size() + 1
+func (self *IAVLNode) calc_height_and_size(db Db) {
+    self.height = maxUint8(self.left_filled(db).Height(), self.right_filled(db).Height()) + 1
+    self.size = self.left_filled(db).Size() + self.right_filled(db).Size() + 1
 }
 
-func (self *IAVLNode) calc_balance() int {
+func (self *IAVLNode) calc_balance(db Db) int {
     if self == nil {
         return 0
     }
-    return int(self.left.Height()) - int(self.right.Height())
+    return int(self.left_filled(db).Height()) - int(self.right_filled(db).Height())
 }
 
-func (self *IAVLNode) balance() (new_self *IAVLNode) {
-    balance := self.calc_balance()
+func (self *IAVLNode) balance(db Db) (new_self *IAVLNode) {
+    balance := self.calc_balance(db)
     if (balance > 1) {
-        if (self.left.calc_balance() >= 0) {
+        if (self.left_filled(db).calc_balance(db) >= 0) {
             // Left Left Case
-            return self.rotate_right()
+            return self.rotate_right(db)
         } else {
             // Left Right Case
             self = self.Copy()
-            self.left = self.left.rotate_left()
+            self.left = self.left_filled(db).rotate_left(db)
             //self.calc_height_and_size()
-            return self.rotate_right()
+            return self.rotate_right(db)
         }
     }
     if (balance < -1) {
-        if (self.right.calc_balance() <= 0) {
+        if (self.right_filled(db).calc_balance(db) <= 0) {
             // Right Right Case
-            return self.rotate_left()
+            return self.rotate_left(db)
         } else {
             // Right Left Case
             self = self.Copy()
-            self.right = self.right.rotate_right()
+            self.right = self.right_filled(db).rotate_right(db)
             //self.calc_height_and_size()
-            return self.rotate_left()
+            return self.rotate_left(db)
         }
     }
     // Nothing changed
@@ -319,7 +333,7 @@ func (self *IAVLNode) balance() (new_self *IAVLNode) {
 }
 
 // TODO: don't clear the hash if the value hasn't changed.
-func (self *IAVLNode) Put(key Key, value Value) (_ *IAVLNode, updated bool) {
+func (self *IAVLNode) Put(db Db, key Key, value Value) (_ *IAVLNode, updated bool) {
     if self == nil {
         return &IAVLNode{key: key, value: value, height: 1, size: 1, hash: nil}, false
     }
@@ -332,38 +346,38 @@ func (self *IAVLNode) Put(key Key, value Value) (_ *IAVLNode, updated bool) {
     }
 
     if key.Less(self.key) {
-        self.left, updated = self.left.Put(key, value)
+        self.left, updated = self.left_filled(db).Put(db, key, value)
     } else {
-        self.right, updated = self.right.Put(key, value)
+        self.right, updated = self.right_filled(db).Put(db, key, value)
     }
     if updated {
         return self, updated
     } else {
-        self.calc_height_and_size()
-        return self.balance(), updated
+        self.calc_height_and_size(db)
+        return self.balance(db), updated
     }
 }
 
-func (self *IAVLNode) Remove(key Key) (new_self *IAVLNode, value Value, err error) {
+func (self *IAVLNode) Remove(db Db, key Key) (new_self *IAVLNode, value Value, err error) {
     if self == nil {
         return nil, nil, NotFound(key)
     }
 
     if self.key.Equals(key) {
         if self.left != nil && self.right != nil {
-            if self.left.Size() < self.right.Size() {
-                self, new_self = self.pop_node(self.right.lmd())
+            if self.left_filled(db).Size() < self.right_filled(db).Size() {
+                self, new_self = self.pop_node(db, self.right_filled(db).lmd(db))
             } else {
-                self, new_self = self.pop_node(self.left.rmd())
+                self, new_self = self.pop_node(db, self.left_filled(db).rmd(db))
             }
             new_self.left = self.left
             new_self.right = self.right
-            new_self.calc_height_and_size()
+            new_self.calc_height_and_size(db)
             return new_self, self.value, nil
         } else if self.left == nil {
-            return self.right, self.value, nil
+            return self.right_filled(db), self.value, nil
         } else if self.right == nil {
-            return self.left, self.value, nil
+            return self.left_filled(db), self.value, nil
         } else {
             return nil, self.value, nil
         }
@@ -374,8 +388,8 @@ func (self *IAVLNode) Remove(key Key) (new_self *IAVLNode, value Value, err erro
             return self, nil, NotFound(key)
         }
         var new_left *IAVLNode
-        new_left, value, err = self.left.Remove(key)
-        if new_left == self.left { // not found
+        new_left, value, err = self.left_filled(db).Remove(db, key)
+        if new_left == self.left_filled(db) { // not found
             return self, nil, err
         } else if err != nil { // some other error
             return self, value, err
@@ -387,8 +401,8 @@ func (self *IAVLNode) Remove(key Key) (new_self *IAVLNode, value Value, err erro
             return self, nil, NotFound(key)
         }
         var new_right *IAVLNode
-        new_right, value, err = self.right.Remove(key)
-        if new_right == self.right { // not found
+        new_right, value, err = self.right_filled(db).Remove(db, key)
+        if new_right == self.right_filled(db) { // not found
             return self, nil, err
         } else if err != nil { // some other error
             return self, value, err
@@ -396,8 +410,8 @@ func (self *IAVLNode) Remove(key Key) (new_self *IAVLNode, value Value, err erro
         self = self.Copy()
         self.right = new_right
     }
-    self.calc_height_and_size()
-    return self.balance(), value, err
+    self.calc_height_and_size(db)
+    return self.balance(db), value, err
 }
 
 func (self *IAVLNode) Height() uint8 {
@@ -419,12 +433,12 @@ func (self *IAVLNode) _md(side func(*IAVLNode)*IAVLNode) (*IAVLNode) {
     }
 }
 
-func (self *IAVLNode) lmd() (*IAVLNode) {
-    return self._md(func(node *IAVLNode)*IAVLNode { return node.left })
+func (self *IAVLNode) lmd(db Db) (*IAVLNode) {
+    return self._md(func(node *IAVLNode)*IAVLNode { return node.left_filled(db) })
 }
 
-func (self *IAVLNode) rmd() (*IAVLNode) {
-    return self._md(func(node *IAVLNode)*IAVLNode { return node.right })
+func (self *IAVLNode) rmd(db Db) (*IAVLNode) {
+    return self._md(func(node *IAVLNode)*IAVLNode { return node.right_filled(db) })
 }
 
 func maxUint8(a, b uint8) uint8 {
diff --git a/merkle/iavl_test.go b/merkle/iavl_test.go
index d57d5c139..295c1f17c 100644
--- a/merkle/iavl_test.go
+++ b/merkle/iavl_test.go
@@ -60,11 +60,11 @@ func TestImmutableAvlPutHasGetRemove(t *testing.T) {
     for i := range records {
         r := randomRecord()
         records[i] = r
-        tree, updated = tree.Put(r.key, String(""))
+        tree, updated = tree.Put(nil, r.key, String(""))
         if updated {
             t.Error("should have not been updated")
         }
-        tree, updated = tree.Put(r.key, r.value)
+        tree, updated = tree.Put(nil, r.key, r.value)
         if !updated {
             t.Error("should have been updated")
         }
@@ -74,13 +74,13 @@ func TestImmutableAvlPutHasGetRemove(t *testing.T) {
     }
 
     for _, r := range records {
-        if has := tree.Has(r.key); !has {
+        if has := tree.Has(nil, r.key); !has {
             t.Error("Missing key")
         }
-        if has := tree.Has(randstr(12)); has {
+        if has := tree.Has(nil, randstr(12)); has {
             t.Error("Table has extra key")
         }
-        if val, err := tree.Get(r.key); err != nil {
+        if val, err := tree.Get(nil, r.key); err != nil {
             t.Error(err, val.(String), r.value)
         } else if !(val.(String)).Equals(r.value) {
             t.Error("wrong value")
@@ -88,19 +88,19 @@ func TestImmutableAvlPutHasGetRemove(t *testing.T) {
     }
 
     for i, x := range records {
-        if tree, val, err = tree.Remove(x.key); err != nil {
+        if tree, val, err = tree.Remove(nil, x.key); err != nil {
             t.Error(err)
         } else if !(val.(String)).Equals(x.value) {
             t.Error("wrong value")
         }
         for _, r := range records[i+1:] {
-            if has := tree.Has(r.key); !has {
+            if has := tree.Has(nil, r.key); !has {
                 t.Error("Missing key")
             }
-            if has := tree.Has(randstr(12)); has {
+            if has := tree.Has(nil, randstr(12)); has {
                 t.Error("Table has extra key")
             }
-            if val, err := tree.Get(r.key); err != nil {
+            if val, err := tree.Get(nil, r.key); err != nil {
                 t.Error(err)
             } else if !(val.(String)).Equals(r.value) {
                 t.Error("wrong value")
@@ -178,7 +178,7 @@ func TestGriffin(t *testing.T) {
             left: l,
             right: r,
         }
-        n.calc_height_and_size()
+        n.calc_height_and_size(nil)
         n.Hash()
         return n
     }
@@ -189,11 +189,11 @@ func TestGriffin(t *testing.T) {
         if n.left == nil && n.right == nil {
             return fmt.Sprintf("%v", n.key)
         } else if n.left == nil {
-            return fmt.Sprintf("(- %v %v)", n.key, P(n.right))
+            return fmt.Sprintf("(- %v %v)", n.key, P(n.right_filled(nil)))
         } else if n.right == nil {
-            return fmt.Sprintf("(%v %v -)", P(n.left), n.key)
+            return fmt.Sprintf("(%v %v -)", P(n.left_filled(nil)), n.key)
         } else {
-            return fmt.Sprintf("(%v %v %v)", P(n.left), n.key, P(n.right))
+            return fmt.Sprintf("(%v %v %v)", P(n.left_filled(nil)), n.key, P(n.right_filled(nil)))
         }
     }
 
@@ -218,7 +218,7 @@ func TestGriffin(t *testing.T) {
     }
 
     expectPut := func(n *IAVLNode, i int, repr string, hashCount uint64) {
-        n2, updated := n.Put(Int32(i), nil)
+        n2, updated := n.Put(nil, Int32(i), nil)
         // ensure node was added & structure is as expected.
         if updated == true || P(n2) != repr {
             t.Fatalf("Adding %v to %v:\nExpected         %v\nUnexpectedly got %v updated:%v",
@@ -229,7 +229,7 @@ func TestGriffin(t *testing.T) {
     }
 
     expectRemove := func(n *IAVLNode, i int, repr string, hashCount uint64) {
-        n2, value, err := n.Remove(Int32(i))
+        n2, value, err := n.Remove(nil, Int32(i))
         // ensure node was added & structure is as expected.
         if value != nil || err != nil || P(n2) != repr {
             t.Fatalf("Removing %v from %v:\nExpected         %v\nUnexpectedly got %v value:%v err:%v",
diff --git a/merkle/types.go b/merkle/types.go
index 4f99383ac..ecd1b0ca0 100644
--- a/merkle/types.go
+++ b/merkle/types.go
@@ -27,21 +27,26 @@ type Tree interface {
     Remove(Key)     (Value, error)
 }
 
+type Db interface {
+    Get([]byte) ([]byte, error)
+    Put([]byte, []byte) error
+}
+
 type Node interface {
     Key()           Key
     Value()         Value
-    Left()          Node
-    Right()         Node
+    Left(Db)        Node
+    Right(Db)       Node
 
     Size()          uint64
     Height()        uint8
-    Has(Key)        bool
-    Get(Key)        (Value, error)
+    Has(Db, Key)    bool
+    Get(Db, Key)    (Value, error)
     Hash()          ([]byte, uint64)
     Bytes()         []byte
 
-    Put(Key, Value) (*IAVLNode, bool)
-    Remove(Key)     (*IAVLNode, Value, error)
+    Put(Db, Key, Value) (*IAVLNode, bool)
+    Remove(Db, Key) (*IAVLNode, Value, error)
 }
 
 type NodeIterator func() Node
diff --git a/merkle/util.go b/merkle/util.go
index c2076bbfa..41bbfa7c8 100644
--- a/merkle/util.go
+++ b/merkle/util.go
@@ -12,11 +12,11 @@ func Iterator(node Node) NodeIterator {
         if len(stack) > 0 || cur != nil {
             for cur != nil {
                 stack = append(stack, cur)
-                cur = cur.Left()
+                cur = cur.Left(nil)
             }
             stack, cur = pop(stack)
             tn = cur
-            cur = cur.Right()
+            cur = cur.Right(nil)
             return tn
         } else {
             return nil
@@ -47,8 +47,8 @@ func printIAVLNode(node *IAVLNode, indent int) {
     if node == nil {
         fmt.Printf("%s--\n", indentPrefix)
     } else {
-        printIAVLNode(node.left, indent+1)
+        printIAVLNode(node.left_filled(nil), indent+1)
         fmt.Printf("%s%v:%v\n", indentPrefix, node.key, node.height)
-        printIAVLNode(node.right, indent+1)
+        printIAVLNode(node.right_filled(nil), indent+1)
     }
 }