PLATE I 
A. —Orange seedlings grown in calcium-free Hoagland’s solution. At tlie end of 
two weeks the full amount of calcium of Hoagland’s solution was added in the form 
of calcimn nitrate. The point at which recovery occurred is seen on each root. 
B. —Showing the point of recovery of roots of orange seedlings (PI. i, A) when 
calcium is added to the solution after two weeks’ exposure to calcium-free Hoagland’s 
solution. 
(7S8) 
