70 BOTANICAL GAZETTE [SEPTEMBER 
Experiment 12.—The methods used in this experiment were 
similar to those used in the previous experiments. The root tips 
were grown at room temperature in the dark in 125 cc. Erlenmeyer 
- flasks of Pyrex glass containing so cc. of solution. The original 
excised primary roots were grown for the first period in the modified 
Pfeffer’s solution plus 2 per cent glucose, and in the same solution 
plus 80, 200, 400, or 800 ppm of autolized yeast or 200 ppm of Gold 
Label gelatine, and transferred to fresh solutions of the same com- 
position as in the first period. Further transfers were made as 
indicated in tableIV. In addition, one set of root tips was grown for 
six weeks in the Pfeffer’s solution containing 2 per cent dextrose 
without transferring, and one set was grown in the same solution 
plus 400 ppm of autolized yeast for six weeks without severing the 
tips, and transferring. 
The autolized yeast extract used in experiment 12 was prepared 
by thoroughly boiling 2 gm. of autolized yeast with roo cc. of dis- 
tilled water, filtering, and making up to the original volume with 
distilled water. This 2 per cent extract of the autolized yeast 
actually contained 0.3366 gm. of dry matter per socc., of which 
0.0525 gm. was ash. An extract prepared in the same way was also 
used in experiment 14. The actual concentration of autolized yeast 
in the nutrient solutions to which yeast was added was about one- 
third of the concentrations given, which are based on the weight of 
the dry yeast as it came from the bottle. Table V indicates the 
approximate amounts of dry material, organic matter, and ash 
added to the culture flasks in the form of the yeast extract. 
The data in table IV and the graphic representation of the 
lengths in fig. 7 show that during the first period the autolized yeast 
exerted no favorable influence on the growth of the roots. It was 
not until near the end of the second period that the beneficial effect 
of the yeast became evident. As was noted earlier, growth in the 
Pfeffer’s solution plus 2 per cent dextrose fell off very markedly in 
the second period, and stopped in the third. In the presence of 
autolized yeast, however, the roots grew in the third and fourth 
periods. The number which could be transferred was decidedly 
reduced in the fourth period, however, but those which were trans- 
ferred made some growth in the fifth period, and some of the roots 
