1922] ROBBINS—ROOT TIPS AND STEM TIPS 385 
and the gain in dry weight compared with the check was twice 
as great. Although the number of corn root and stem tips used in 
this experiment was small, the roots grown in glucose were better 
than those in levulose. No comparison between the two sugars 
could be made in the case of cotton stem tips. The contrast between 
the relative effect of glucose and levulose on the amount of growth 
made by the tissue of these seed plants and their effect upon the 
TABLE IV 
GROWTH OF SHOOT Act OF PEA AND CORN IN DARK, tater nipilanre AND ELEVEN DAYS 
PECTIVELY, IN STERILE NUTRIENT SOLUTION: 
Additions to modified Number shoot ~~ al Gain in Total number 
Pfeffer’s solution tips used neat hap ) length (cm.) roots 
Peas 
ee ee 15 "7k 12.77 7 
Levulos Se) civ ae 15 1.72 3-58 3 
OR a a 14 17 0.88 14 
Corn 
Cilacese (695) 205i) a es 3 2.16 17.5 13 
-oetetaagl ac wi, 3 fae ee ek eo 3 2.90 12.43 8 
NONG. oie ae 2 3-75 4.50 . 
growth made by Ceratodon purpureus should be noted. In the case 
of the latter plant, as reported earlier (13), the amount of dry matter 
produced with levulose as the carbon source was 2-7 times as great 
as the amount produced with glucose. The fact that the stem tips 
in the dark, even in the presence of 2 per cent glucose, are morpho- 
logically like etiolated shoots, would also indicate that it is not an 
absence of available carbohydrate which causes the stem elongation 
and small leaf development of plants grown in the dark. 
Continued growth of root tips in culture solutions 
The fact that the root tips in these experiments grew in solutions 
containing carbohydrates, and made very little growth in the same 
solutions lacking sugar, would suggest that the complete require- 
ments for the growth of roots are water, mineral salts, carbohy- 
drates, and free oxygen. If such were the case we should expect 
