466 BROOKLYN BOTANIC GARDEN MEMOIRS 



surface area of the organs in touch with the same. Inasmuch as the 

 plants used were seedhngs 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 



