diff --git a/Lib/src/com/yarcat/chemistrylines/field/Cell.java b/Lib/src/com/yarcat/chemistrylines/field/Cell.java
index 5958695..a0d148c 100644
--- a/Lib/src/com/yarcat/chemistrylines/field/Cell.java
+++ b/Lib/src/com/yarcat/chemistrylines/field/Cell.java
@@ -1,9 +1,20 @@
 package com.yarcat.chemistrylines.field;
 
+import java.util.EnumSet;
+
 /** Represents a cell in a game field. */
 public final class Cell {
 
+    // @formatter:off
+    public enum Mark {
+        SelectedAsSource,
+        SelectedAsDestination,
+        ReachableFromSource,
+    }
+    // @formatter:on
+
     private Element mElement = null;
+    private EnumSet<Mark> x;
 
     public boolean isEmpty() {
         return getElement() == null;
@@ -16,4 +27,18 @@ public void setElement(Element element) {
     public Element getElement() {
         return mElement;
     }
-}
\ No newline at end of file
+
+    public void setMark(Mark m) {
+        x.add(m);
+    }
+
+    public void clearMark(Mark m) {
+        if (x.contains(m)) {
+            x.remove(m);
+        }
+    }
+
+    public boolean hasMark(Mark m) {
+        return x.contains(m);
+    }
+}
diff --git a/Lib/src/com/yarcat/chemistrylines/field/Field.java b/Lib/src/com/yarcat/chemistrylines/field/Field.java
index 659187c..895df50 100644
--- a/Lib/src/com/yarcat/chemistrylines/field/Field.java
+++ b/Lib/src/com/yarcat/chemistrylines/field/Field.java
@@ -1,5 +1,8 @@
 package com.yarcat.chemistrylines.field;
 
+import com.yarcat.chemistrylines.algorithms.Path;
+import com.yarcat.chemistrylines.field.Cell.Mark;
+import com.yarcat.chemistrylines.view.SelectionInView.SelectionListener;
 
 /** Game field (model) interface. */
 public interface Field {
@@ -41,7 +44,7 @@ public interface SequenceVisitor {
     public void removeCompound(int[] cells);
 
     /* Implementation of functionality common for all fields */
-    public static abstract class BaseField implements Field {
+    public static abstract class BaseField implements Field, SelectionListener {
 
         @Override
         public void removeCompound(int[] cells) {
@@ -49,5 +52,47 @@ public void removeCompound(int[] cells) {
                 at(n).setElement(null);
             }
         }
+
+        @Override
+        public void onNewSource(int n) {
+            if (n > -1) {
+                at(n).setMark(Mark.SelectedAsSource);
+                markCellsReachableFrom(n);
+            }
+        }
+
+        @Override
+        public void onNewDestination(int n) {
+            if (n > -1) {
+                at(n).setMark(Mark.SelectedAsDestination);
+            }
+        }
+
+        @Override
+        public void onSelectionCleared(int s, int d) {
+            if (s > -1) {
+                at(s).clearMark(Mark.SelectedAsSource);
+                clearCellsReachableFrom(s);
+            }
+            if (d > -1) {
+                at(d).clearMark(Mark.SelectedAsSource);
+            }
+        }
+
+        private void markCellsReachableFrom(int n) {
+            Path p = new Path(this, n);
+            p.evaluate();
+            for (int i = 0; i < getLength(); ++i) {
+                if (p.isReachable(i)) {
+                    at(i).setMark(Mark.ReachableFromSource);
+                }
+            }
+        }
+
+        private void clearCellsReachableFrom(int n) {
+            for (int i = 0; i < getLength(); ++i) {
+                at(i).clearMark(Mark.ReachableFromSource);
+            }
+        }
     }
 }
diff --git a/Lib/src/com/yarcat/chemistrylines/view/SelectionInView.java b/Lib/src/com/yarcat/chemistrylines/view/SelectionInView.java
index 00a9a11..a316983 100644
--- a/Lib/src/com/yarcat/chemistrylines/view/SelectionInView.java
+++ b/Lib/src/com/yarcat/chemistrylines/view/SelectionInView.java
@@ -1,18 +1,37 @@
 package com.yarcat.chemistrylines.view;
 
 public class SelectionInView {
+    public interface SelectionListener {
+
+        public void onNewSource(int n);
+
+        public void onNewDestination(int n);
+
+        public void onSelectionCleared(int src, int dst);
+    }
+
+    private SelectionListener mListener;
     private int[] mSelection = new int[] { -1, -1 };
 
     public void select(int n) {
         if (mSelection[0] == -1) {
             mSelection[0] = n;
+            if (mListener != null) {
+                mListener.onNewSource(n);
+            }
         } else {
             mSelection[1] = n;
+            if (mListener != null) {
+                mListener.onNewDestination(n);
+            }
         }
     }
 
     public void clear() {
         mSelection[0] = mSelection[1] = -1;
+        if (mListener != null) {
+            mListener.onSelectionCleared(mSelection[0], mSelection[1]);
+        }
     }
 
     public boolean hasSource() {
@@ -30,4 +49,8 @@ public boolean hasDestination() {
     public int getDestination() {
         return mSelection[1];
     }
+
+    public void setListener(SelectionListener l) {
+        mListener = l;
+    }
 }