278 BOTANICAL GAZETTE [APRIL 
TABLE XVII—Continued 
SEEDS Coats ENDOSPERM EMBRYO 
Oenothera biennis 
PNY ores Partly acid Slightly acid or neutral | Cell walls acid; con- 
tents neutra 
haute Mostly acid Slightly acid to neutral | Cell walls acid to neu- 
tral; contents alkaline 
to neutral 
Soaked in light. .| Partly acid Neutral to acid Walls and contents acid 
Quantitative determination of acidity 
To verify the results of the microchemical examination, 5 gm. 
of each kind of seed incubated in light for five days and 5 gm. of 
each kind incubated in darkness for five days were separately 
ground, digested in neutral alcohol and ether, and then titrated 
with N/1to NaOH. The results obtained were as follows: 
Seed Light Darkness 
PMO CNS es +. 5.0 2.8 cc 
DRC CAM a ae 2.8 
Verbascum Thapsus............ 4. 3 4.4 
 Nipotiana Tabactim. .......4..> 3-9 2.8 
These results show greater acidity of seeds incubated in light 
than of those incubated in darkness, and confirm the findings of 
the microchemical examination. While the increase of titratable 
acidity was not large, it was measurable and repeatedly obtained, 
and apparently was sufficient in each instance to determine germina- 
tion. Since light is the variable factor in this and the preceding 
experiment, we may properly conclude that light initiates changes 
which produce the increased acidity of seeds incubated in light 
over those incubated in darkness. These results establish the fact 
that light functions in some way to bring about increased acidity in 
these light-sensitive seeds. There remains to show in the following 
experiment, if possible, how the acidity is increased. 
Effect of germination on substratum 
Having found that the embryos of these seeds become acid in 
reaction by incubation in light, it was thought that testing the 
