1922] ROBBINS—ROOT TIPS AND STEM TIPS 379 
The former floated on water, the latter sank. The average growth 
in length of the roots is given in table I, from which it can be noted 
Fic. 1.—Appearance of root tips of corn in Pfeffer’s solution at end of twenty- 
four days; flask no. 1 contains 2 per cent glucose, flask no. 2 contains no carbohydrates; 
root tip in no. appeared as root tip does in no. 2 at beginning of experiment. 
that in the mineral nutrient solution alone the average gain in 
length was 0.84 cm., and no secondary roots were produced. In 
levulose the avereae gain was 2.04 cm. with 2.3 secondary roots; 
TABLE I 
Roor TIPS OF PEA GROWN TWENTY-NINE DAYS IN DARK 
i peraee — in length Side roots 
Solution Number root original 9 day - | Avecage' number 
tips used length gan sey da per 
—? 
Pfeffer’s solution sss | 13 1. 0.84 ° 
Seiier's plus ms ucose. on 14 1.40 4.27 $.5 
feffer’s plus levulose...... £5 1.54 2.04 2.3 
in glucose the average gain was 4.27 cm. with 3.5 secondary roots. 
Considerable variation in growth was evident. Some of the roots 
