1922] | ; ROBBINS—ROOT TIPS 63 
yeast growth stopped in the third two-week period. Autolized yeast 
appeared to be somewhat more favorable than peptone. The 
details of these two experiments are as follows. 
Experiment 5.—In this experiment the method of culture was as 
previously described. Grains of Longfellow flint corn were sterilized 
by Witson’s hypochlorite method. The excised tips of the original 
primary roots were grown in the modified Pfeffer’s solution plus 2 
Fic, 2.—Effect of peptone at end of second period on growth of corn root tips in 
dark; two root tips on left in Pfeffer’s solution plus 2 per cent glucose, two on right in 
same solution plus about 400 ppm peptone. 
per cent glucose. The root tips of these excised roots were cut off 
after eleven days and transferred to the same solution, to the same 
solution plus peptone, or to the same solution plus autolized yeast. 
Further transfers were made as indicated in table II. Erlenmeyer 
flasks of 125 cc. capacity containing 50 cc. of solution were used. 
One cc. of a sterile 2 per cent solution of Difco peptone was added to 
each flask containing peptone, and 1 cc. of a sterile 1 per cent auto- 
lized yeast suspension was added to each flask containing auto- 
lized yeast. This produced solutions containing approximately 
