466 BROOKLYN BOTANIC GARDEN MEMOIRS 
surface area of the organs in touch with the same. Inasmuch as the 
plants used were seedlings and a larger number were employed than 
in the preceding series, the results are likely to be more uniform. 
On the other hand it should be noted that with the use of seedlings 
grown under good heat conditions (in which case they would develop 
rapidly) the duration of stimulus would be much less prolonged, and 
the ultimate effect of contact on the configuration of the plants 
would be less pronounced. The most marked stimulating effect of 
contact would occur in general in those experiments which were the 
most prolonged, namely with the larger seedlings. With the excep- 
tion of corn all of the measurements given are either of the hypocotyls 
or stems. The results of these experiments are given in Tables 10-15, 
all of which show a stimulated growth due to contact with excelsior. 
The average weight in all instances where determined was greater 
in the contact than in the normal. In one water determination with 
lupine, there was 4 percent more moisture in the contact-stimulated 
plants than in the normal. In the experiments with corn (Table 14) 
measurements of leaves were taken as well as the cotyledons although 
it was our original intention to include in our measurements the 
cotyledons only, since when the leaves break through the cotyledons 
the growth of these organs is greatly retarded. The data giving the 
measurements of leaves in the corn, however, have a limited value as 
the growth of the leaves displayed more or less erratic behavior. In 
one experiment the leaves protruded above the excelsior and conse- 
quently they were not in contact. In another instance the leaves 
showed a very decidedly accelerated growth in the normal plants 
which was caused by a brief and accidental exposure to light. By 
taking proper precautions in further experiments this did not occur 
again. Some of the more sensitive cotyledons of the Gramineae are 
characterized by a marked growth correlation following mutilation 
or decapitation of the cotyledons in etiolated seedlings, and similar 
reactions occur to etiolated seedlings which are exposed to light. 
The function apparently of the cotyledons is to protect the true 
leaves in protruding upwards through the soil and as soon as they 
are exposed to light their growth ceases rather abruptly. Correlated 
with the retarded growth of the cotyledons is a greatly accelerated 
growth of the leaves which may amount to over 100 percent increase 
in two or three hours. The exposure of the cotyledons to light even 
for a brief period is sufficient to check their growth and greatly ac- 
celerate the development of the leaves and this is what happened on 
one occasion. 
The normal plants would be the most affected by any such exposure 
as they were not covered with excelsior, while the contact plants 
