172 KANSAS ACADEMY OF SCIENCE. 



storm; for the wind would pass more freely through them, and less injury would be 

 likely to result from breakage or mutilation. This would be more emphatically true 

 in the case of submerged water plants. The finely-dissected foliage would offer less 

 resistance to the passage of water through it; it would sway in unison with the 

 motion of the water, and the injury would certainly be reduced to a minimum, while 

 if the leaves were large it seems obvious that they would be more or less mutilated 

 or injured by the action of the water. 



It has been suggested that this tendency towards division might, in part at least. 

 be referable to the agency of insects. The large leaves not only offer more food in 

 compact space, but also afford good standing-ground for the insects while feeding: 

 besides, leaf-rollers could make better use of large leaves than finely-divided ones. 



With a view of determining whether this suggestion has any foundation in fact, 

 I prepared a list of the commonest plants in the immediate vicinity t)f Manhattan 

 that bear large leaves, comprising the following genera: 



^SCUlUS. 



Arctium. 



Asimina. 



Cacalia. 



Catalpa. 



Celastnis. 



Celtls. 



Another list was made of plants in the same region, with very small leaves, or the 



blades of which were much divided. This second list included the following genera: 



Acer. Cassia. Houston ia. Robinia. 



Achillea. Delphinium. Hymenopappus. Rosa. 



Aquilegia. Desmanthns. Leptocaulis. Salix. 



Ambrosia. Ellisia, Lygodesmia. Schrankia. 



Amorpha. Galium. Lythrum. Symphoricarpus. 



Artemisia. Geranium. Melilotus. Thalictrum. 



Astralagus. Hibiscus. Pronalea. 



These two lists were handed to an entomologist, with the request that he enumer- 

 ate the species of insects reported as attacking the several species belonging to the 

 genera. An examination of the enumerated lists revealed the fact, that in case of 

 some of the genera not a single insect while in others as many as twenty insects 

 have been reported as attacking the plants. 



The total number of insects on the plants with large leaves was l(t4. The total 

 number on the plants with small leaves was 152; but, before proceeding further, it 

 may be well to say that the genus Quercus was at first included in the list of large 

 leaves, but was subsequently rejected. For this exclusion there seemed to be two. 

 perhaps, suflficient reasons: First, while in some of the oaks the leaves are large and 

 full, in many others they are comparatively small or the blade is cut into medium- 

 sized or small segments. In the second place, only two species of oaks ( Q. jvimoides 

 and Q. macrocarpa) are very abundant, and three others, {Q. nigra. Q. rubr-a. and 

 Q. tinetorku) moderately abundant in the region which furnished the genera of the 

 foregoing lists; and it is evident that of the 117 species of insects reported (>n the 

 oak, a comparatively few of them should be credited to this district. As stated above, 

 the plants with large leaves harbor less instead of more insects than those with the 

 small leaves, as was suggested. That plants with small leaves should harbor a 

 greater number of insects might possibly be explained by reference to the fact that 

 the smaller leaves are usually somewhat more tender, at least have a lighter or less 

 woody framework or skeleton, iuid therefore, perha]is. furnish more enticing food 

 for insects. 



In closing, it may then be remarked that the supposition that the present forms 

 of leaves are both the former and tlie ultimate ones, is entirely erroneous. Paleon- 

 tology demonstrates the fact of a long history of a gradual change of forms, and the 

 study detailed above suggests what is going on now. The future forms, therefore, 

 will be the resultant of the environment acting on these variable organs. 



