diff --git a/d3.layout.js b/d3.layout.js
index c9f0b1cd..f0f844c4 100644
--- a/d3.layout.js
+++ b/d3.layout.js
@@ -529,17 +529,13 @@ d3.layout.partition = function() {
     return nodes;
   }
 
-  partition.sort = d3.rebind(partition, hierarchy.sort);
-  partition.children = d3.rebind(partition, hierarchy.children);
-  partition.value = d3.rebind(partition, hierarchy.value);
-
   partition.size = function(x) {
     if (!arguments.length) return size;
     size = x;
     return partition;
   };
 
-  return partition;
+  return d3_layout_hierarchyRebind(partition, hierarchy);
 };
 d3.layout.pie = function() {
   var value = Number,
@@ -1054,6 +1050,15 @@ d3.layout.hierarchy = function() {
   return hierarchy;
 }
 
+// A method assignment helper for hierarchy subclasses.
+function d3_layout_hierarchyRebind(object, hierarchy) {
+  object.sort = d3.rebind(object, hierarchy.sort);
+  object.children = d3.rebind(object, hierarchy.children);
+  object.links = d3_layout_hierarchyLinks;
+  object.value = d3.rebind(object, hierarchy.value);
+  return object;
+}
+
 function d3_layout_hierarchyChildren(d) {
   return d.children;
 }
@@ -1065,8 +1070,17 @@ function d3_layout_hierarchyValue(d) {
 function d3_layout_hierarchySort(a, b) {
   return b.value - a.value;
 }
+
+// Returns an array source+target objects for the specified nodes.
+function d3_layout_hierarchyLinks(nodes) {
+  return d3.merge(nodes.map(function(parent) {
+    return (parent.children || []).map(function(child) {
+      return {source: parent, target: child};
+    });
+  }));
+}
 d3.layout.pack = function() {
-  var hierarchy = d3.layout.hierarchy(),
+  var hierarchy = d3.layout.hierarchy().sort(d3_layout_packSort),
       size = [1, 1];
 
   function pack(d, i) {
@@ -1087,17 +1101,13 @@ d3.layout.pack = function() {
     return nodes;
   }
 
-  pack.sort = d3.rebind(pack, hierarchy.sort);
-  pack.children = d3.rebind(pack, hierarchy.children);
-  pack.value = d3.rebind(pack, hierarchy.value);
-
   pack.size = function(x) {
     if (!arguments.length) return size;
     size = x;
     return pack;
   };
 
-  return pack.sort(d3_layout_packSort);
+  return d3_layout_hierarchyRebind(pack, hierarchy);
 };
 
 function d3_layout_packSort(a, b) {
@@ -1310,10 +1320,6 @@ d3.layout.cluster = function() {
     return nodes;
   }
 
-  cluster.sort = d3.rebind(cluster, hierarchy.sort);
-  cluster.children = d3.rebind(cluster, hierarchy.children);
-  cluster.links = d3_layout_treeLinks;
-
   cluster.separation = function(x) {
     if (!arguments.length) return separation;
     separation = x;
@@ -1326,7 +1332,7 @@ d3.layout.cluster = function() {
     return cluster;
   };
 
-  return cluster;
+  return d3_layout_hierarchyRebind(cluster, hierarchy);
 };
 
 function d3_layout_clusterY(children) {
@@ -1465,7 +1471,7 @@ d3.layout.tree = function() {
         deep = d3_layout_treeSearch(root, d3_layout_treeDeepest),
         x0 = left.x - separation(left, right) / 2,
         x1 = right.x + separation(right, left) / 2,
-        y1 = deep.depth;
+        y1 = deep.depth || 1;
 
     // Clear temporary layout variables; transform x and y.
     d3_layout_treeVisitAfter(root, function(node) {
@@ -1477,10 +1483,6 @@ d3.layout.tree = function() {
     return nodes;
   }
 
-  tree.sort = d3.rebind(tree, hierarchy.sort);
-  tree.children = d3.rebind(tree, hierarchy.children);
-  tree.links = d3_layout_treeLinks;
-
   tree.separation = function(x) {
     if (!arguments.length) return separation;
     separation = x;
@@ -1493,18 +1495,9 @@ d3.layout.tree = function() {
     return tree;
   };
 
-  return tree;
+  return d3_layout_hierarchyRebind(tree, hierarchy);
 };
 
-// Returns an array source+target objects for the specified nodes.
-function d3_layout_treeLinks(nodes) {
-  return d3.merge(nodes.map(function(parent) {
-    return (parent.children || []).map(function(child) {
-      return {source: parent, target: child};
-    });
-  }));
-}
-
 function d3_layout_treeSeparation(a, b) {
   return a.parent == b.parent ? 1 : 2;
 }
@@ -1740,10 +1733,6 @@ d3.layout.treemap = function() {
     return nodes;
   }
 
-  treemap.sort = d3.rebind(treemap, hierarchy.sort);
-  treemap.children = d3.rebind(treemap, hierarchy.children);
-  treemap.value = d3.rebind(treemap, hierarchy.value);
-
   treemap.size = function(x) {
     if (!arguments.length) return size;
     size = x;
@@ -1769,6 +1758,6 @@ d3.layout.treemap = function() {
     return treemap;
   };
 
-  return treemap;
+  return d3_layout_hierarchyRebind(treemap, hierarchy);
 };
 })()
\ No newline at end of file
diff --git a/d3.layout.min.js b/d3.layout.min.js
index fb423160..dcab42ef 100644
--- a/d3.layout.min.js
+++ b/d3.layout.min.js
@@ -1 +1 @@
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b=a.children;return b?M(b[b.length-1]):a}function L(a){var b=a.children;return b?L(b[0]):a}function K(a){return a.reduce(function(a,b){return a+b.x},0)/a.length}function J(a){return 1+d3.max(a,function(a){return a.y})}function I(a,b,c){var d=b.r+c.r,e=a.r+c.r,f=b.x-a.x,g=b.y-a.y,h=Math.sqrt(f*f+g*g),i=(e*e+h*h-d*d)/(2*e*h),j=Math.acos(i),k=i*e,l=Math.sin(j)*e;f/=h,g/=h,c.x=a.x+k*f+l*g,c.y=a.y+k*g-l*f}function H(a,b,c,d){var e=a.children;a.x=b+=d*a.x,a.y=c+=d*a.y,a.r*=d;if(e){var f=-1,g=e.length;while(++f<g)H(e[f],b,c,d)}}function G(a){var b=a.children;b?(b.forEach(G),a.r=D(b)):a.r=Math.sqrt(a.value)}function F(a){delete a._pack_next,delete a._pack_prev}function E(a){a._pack_next=a._pack_prev=a}function D(a){function l(a){b=Math.min(a.x-a.r,b),c=Math.max(a.x+a.r,c),d=Math.min(a.y-a.r,d),e=Math.max(a.y+a.r,e)}var 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Math.max(b*e*f/c,c/(b*g*f))}function i(a){if(!!a.children){var b={x:a.x,y:a.y,dx:a.dx,dy:a.dy},c=a.children.slice(),d,e=[];e.area=0;while(d=c.pop())e.push(d),e.area+=d.area,d.z!=null&&(k(e,d.z?b.dx:b.dy,b,!c.length),e.length=e.area=0);a.children.forEach(i)}}function h(a){if(!!a.children){var b={x:a.x,y:a.y,dx:a.dx,dy:a.dy},c=[],d=a.children.slice(),e,f=Infinity,g,i=Math.min(b.dx,b.dy),l;c.area=0;while((l=d.length)>0)c.push(e=d[l-1]),c.area+=e.area,(g=j(c,i))<=f?(d.pop(),f=g):(c.area-=c.pop().area,k(c,i,b,!1),i=Math.min(b.dx,b.dy),c.length=c.area=0,f=Infinity);c.length&&(k(c,i,b,!0),c.length=c.area=0),a.children.forEach(h)}}function g(a,b){var c=a.children;a.area=a.value*b;if(c){var d=-1,e=c.length;while(++d<e)g(c[d],b)}}var a=d3.layout.hierarchy(),b=Math.round,c=[1,1],d=!1,e,f=.5*(1+Math.sqrt(5));l.size=function(a){if(!arguments.length)return c;c=a;return l},l.round=function(a){if(!arguments.length)return b!=Number;b=a?Math.round:Number;return l},l.sticky=function(a){if(!arguments.length)return d;d=a,e=null;return l},l.ratio=function(a){if(!arguments.length)return f;f=a;return l};return w(l,a)}})()
\ No newline at end of file
diff --git a/examples/tree/tree-dynamic.html b/examples/tree/tree-dynamic.html
new file mode 100644
index 00000000..d076c40a
--- /dev/null
+++ b/examples/tree/tree-dynamic.html
@@ -0,0 +1,119 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta http-equiv="Content-Type" content="text/html;charset=utf-8">
+    <title>Node-Link Tree</title>
+    <script type="text/javascript" src="../../d3.js"></script>
+    <script type="text/javascript" src="../../d3.layout.js"></script>
+    <style type="text/css">
+
+.node {
+  stroke: #fff;
+  stroke-width: 2px;
+}
+
+.link {
+  fill: none;
+  stroke: #000;
+}
+
+    </style>
+  </head>
+  <body>
+    <script type="text/javascript">
+
+var w = 960,
+    h = 500,
+    root = {},
+    data = [root],
+    tree = d3.layout.tree().size([w - 20, h - 20]),
+    diagonal = d3.svg.diagonal(),
+    duration = 750,
+    timer = setInterval(update, duration);
+
+var vis = d3.select("body").append("svg:svg")
+    .attr("width", w)
+    .attr("height", h)
+  .append("svg:g")
+    .attr("transform", "translate(10, 10)");
+
+vis.selectAll("circle")
+    .data(tree(root))
+  .enter().append("svg:circle")
+    .attr("class", "node")
+    .attr("r", 3.5)
+    .attr("cx", x)
+    .attr("cy", y);
+
+function update() {
+  if (data.length >= 500) return clearInterval(timer);
+
+  // Add a new datum to a random parent.
+  var d = {id: data.length}, parent = data[~~(Math.random() * data.length)];
+  if (parent.children) parent.children.push(d); else parent.children = [d];
+  data.push(d);
+
+  // Compute the new tree layout. We'll stash the old layout in the data.
+  var nodes = tree(root);
+
+  // Update the nodes…
+  var node = vis.selectAll("circle.node")
+      .data(nodes, nodeId);
+
+  // Enter any new nodes at the parent's previous position.
+  node.enter().append("svg:circle")
+      .attr("class", "node")
+      .attr("r", 3.5)
+      .attr("cx", function(d) { return d.parent.data.x0; })
+      .attr("cy", function(d) { return d.parent.data.y0; })
+    .transition()
+      .duration(duration)
+      .attr("cx", x)
+      .attr("cy", y);
+
+  // Transition nodes to their new position.
+  node.transition()
+      .duration(duration)
+      .attr("cx", x)
+      .attr("cy", y);
+
+  // Update the links…
+  var link = vis.selectAll("path.link")
+      .data(tree.links(nodes), linkId);
+
+  // Enter any new links at the parent's previous position.
+  link.enter().insert("svg:path", "circle")
+      .attr("class", "link")
+      .attr("d", function(d) {
+        var o = {x: d.source.data.x0, y: d.source.data.y0};
+        return diagonal({source: o, target: o});
+      })
+    .transition()
+      .duration(duration)
+      .attr("d", diagonal);
+
+  // Transition links to their new position.
+  link.transition()
+      .duration(duration)
+      .attr("d", diagonal);
+}
+
+function linkId(d) {
+  return d.source.data.id + "-" + d.target.data.id;
+}
+
+function nodeId(d) {
+  return d.data.id;
+}
+
+function x(d) {
+  return d.data.x0 = d.x;
+}
+
+function y(d) {
+  return d.data.y0 = d.y;
+}
+
+    </script>
+  </body>
+</html>
diff --git a/src/layout/cluster.js b/src/layout/cluster.js
index fae458dd..e030f45b 100644
--- a/src/layout/cluster.js
+++ b/src/layout/cluster.js
@@ -39,10 +39,6 @@ d3.layout.cluster = function() {
     return nodes;
   }
 
-  cluster.sort = d3.rebind(cluster, hierarchy.sort);
-  cluster.children = d3.rebind(cluster, hierarchy.children);
-  cluster.links = d3_layout_treeLinks;
-
   cluster.separation = function(x) {
     if (!arguments.length) return separation;
     separation = x;
@@ -55,7 +51,7 @@ d3.layout.cluster = function() {
     return cluster;
   };
 
-  return cluster;
+  return d3_layout_hierarchyRebind(cluster, hierarchy);
 };
 
 function d3_layout_clusterY(children) {
diff --git a/src/layout/hierarchy.js b/src/layout/hierarchy.js
index 46dd4c15..96142881 100644
--- a/src/layout/hierarchy.js
+++ b/src/layout/hierarchy.js
@@ -78,6 +78,15 @@ d3.layout.hierarchy = function() {
   return hierarchy;
 }
 
+// A method assignment helper for hierarchy subclasses.
+function d3_layout_hierarchyRebind(object, hierarchy) {
+  object.sort = d3.rebind(object, hierarchy.sort);
+  object.children = d3.rebind(object, hierarchy.children);
+  object.links = d3_layout_hierarchyLinks;
+  object.value = d3.rebind(object, hierarchy.value);
+  return object;
+}
+
 function d3_layout_hierarchyChildren(d) {
   return d.children;
 }
@@ -89,3 +98,12 @@ function d3_layout_hierarchyValue(d) {
 function d3_layout_hierarchySort(a, b) {
   return b.value - a.value;
 }
+
+// Returns an array source+target objects for the specified nodes.
+function d3_layout_hierarchyLinks(nodes) {
+  return d3.merge(nodes.map(function(parent) {
+    return (parent.children || []).map(function(child) {
+      return {source: parent, target: child};
+    });
+  }));
+}
diff --git a/src/layout/pack.js b/src/layout/pack.js
index 6f1a07ad..527ac27c 100644
--- a/src/layout/pack.js
+++ b/src/layout/pack.js
@@ -1,5 +1,5 @@
 d3.layout.pack = function() {
-  var hierarchy = d3.layout.hierarchy(),
+  var hierarchy = d3.layout.hierarchy().sort(d3_layout_packSort),
       size = [1, 1];
 
   function pack(d, i) {
@@ -20,17 +20,13 @@ d3.layout.pack = function() {
     return nodes;
   }
 
-  pack.sort = d3.rebind(pack, hierarchy.sort);
-  pack.children = d3.rebind(pack, hierarchy.children);
-  pack.value = d3.rebind(pack, hierarchy.value);
-
   pack.size = function(x) {
     if (!arguments.length) return size;
     size = x;
     return pack;
   };
 
-  return pack.sort(d3_layout_packSort);
+  return d3_layout_hierarchyRebind(pack, hierarchy);
 };
 
 function d3_layout_packSort(a, b) {
diff --git a/src/layout/partition.js b/src/layout/partition.js
index aacbf292..171d3fc1 100644
--- a/src/layout/partition.js
+++ b/src/layout/partition.js
@@ -38,15 +38,11 @@ d3.layout.partition = function() {
     return nodes;
   }
 
-  partition.sort = d3.rebind(partition, hierarchy.sort);
-  partition.children = d3.rebind(partition, hierarchy.children);
-  partition.value = d3.rebind(partition, hierarchy.value);
-
   partition.size = function(x) {
     if (!arguments.length) return size;
     size = x;
     return partition;
   };
 
-  return partition;
+  return d3_layout_hierarchyRebind(partition, hierarchy);
 };
diff --git a/src/layout/tree.js b/src/layout/tree.js
index d48cabb3..40452866 100644
--- a/src/layout/tree.js
+++ b/src/layout/tree.js
@@ -113,7 +113,7 @@ d3.layout.tree = function() {
         deep = d3_layout_treeSearch(root, d3_layout_treeDeepest),
         x0 = left.x - separation(left, right) / 2,
         x1 = right.x + separation(right, left) / 2,
-        y1 = deep.depth;
+        y1 = deep.depth || 1;
 
     // Clear temporary layout variables; transform x and y.
     d3_layout_treeVisitAfter(root, function(node) {
@@ -125,10 +125,6 @@ d3.layout.tree = function() {
     return nodes;
   }
 
-  tree.sort = d3.rebind(tree, hierarchy.sort);
-  tree.children = d3.rebind(tree, hierarchy.children);
-  tree.links = d3_layout_treeLinks;
-
   tree.separation = function(x) {
     if (!arguments.length) return separation;
     separation = x;
@@ -141,18 +137,9 @@ d3.layout.tree = function() {
     return tree;
   };
 
-  return tree;
+  return d3_layout_hierarchyRebind(tree, hierarchy);
 };
 
-// Returns an array source+target objects for the specified nodes.
-function d3_layout_treeLinks(nodes) {
-  return d3.merge(nodes.map(function(parent) {
-    return (parent.children || []).map(function(child) {
-      return {source: parent, target: child};
-    });
-  }));
-}
-
 function d3_layout_treeSeparation(a, b) {
   return a.parent == b.parent ? 1 : 2;
 }
diff --git a/src/layout/treemap.js b/src/layout/treemap.js
index 3ef0e17a..7309aa19 100644
--- a/src/layout/treemap.js
+++ b/src/layout/treemap.js
@@ -141,10 +141,6 @@ d3.layout.treemap = function() {
     return nodes;
   }
 
-  treemap.sort = d3.rebind(treemap, hierarchy.sort);
-  treemap.children = d3.rebind(treemap, hierarchy.children);
-  treemap.value = d3.rebind(treemap, hierarchy.value);
-
   treemap.size = function(x) {
     if (!arguments.length) return size;
     size = x;
@@ -170,5 +166,5 @@ d3.layout.treemap = function() {
     return treemap;
   };
 
-  return treemap;
+  return d3_layout_hierarchyRebind(treemap, hierarchy);
 };