1922] ROBBINS—ROOT TIPS AND STEM TIPS 383 
agar, and in Pfeffer’s solution plus 2 per cent glucose containing 
I per cent agar. It can be noted from the figure that the root tip 
not supplied with glucose has made little growth, while the root tip 
supplied with glucose has made considerable growth, has responded 
normally to gravity, and has 
produced a considerable num- 
ber of secondary roots. 
Growth of shoot tips in sterile 
nutrient solutions 
The shoot tips of pea, corn, 
and cotton were placed in the 
three solutions and grown in 
the dark. While growth was 
secured in the carbohydrate 
solution with cotton, the de- 
velopment was abnormal and 
measurements were not made. 
The shoots of peas and corn 
developed more normally in ~— 
the carbohydrate solution, and Fic. 3.—Growth of root tips in Pfeffer’s 
in many cases produced roots, lution plus 1.0 per cent agar; tube on 
The plants howeved were chins left no glucose, tube on right 2 per cent 
’ ’ glucose. 
rotic and showed the elonga- 
tion and small leaf development typical of plants grown in the 
dark (fig. 4). In both cases, as indicated in table IV, the greatest 
increase in length occurred in the glucose solution and least in the 
Pfeffer’s solution without sugar. The relative growth of the shoot 
tips in the three solutions was therefore the same as that of the 
root tips. Starch was found in the tissue grown in the glucose 
and levulose solutions, and in the guard cells of the shoots in the 
Pfeffer’s solution. 
From these experiments it is evident that in the dark, in solution 
cultures containing the mineral salts commonly accepted as essential 
for the growth of green plants and a soluble carbohydrate, the root 
tips of corn, cotton, and peas, and the stem tips of corn, cotton, and 
peas make considerable growth. In the same solutions lacking 
ae eg 
