1884. 389 Trans. N. VY. Aeé...Sét. 
read with much interest by students of natural history; and his theory 
there advanced, that serrated, lobed, and divided leaves have attained 
these forms by struggling with others for their required supply of car- 
bonic acid and sunlight during very long periods of time, by a process 
of gradual change or evolution from an originally entire-margined 
leaf-form, has appeared to us, to say the least, ingenious. 
There are, however, considerations which will not allow us to accept 
this attractive theory without question; to some of these I propose in 
this paper to allude, using familiar examples illustrative of what is 
presented, as well as some observations and ideas of my own, indica- 
tive of what seem to me to be more probable causes by which the 
modification of leaf-forms is effected than those advanced by Mr. 
ALLEN. 
The various marginal and ultra-marginal modifications of leaves— 
the serrations, lobations, divisions, etc.—and their plans of venation 
seem mutually dependent on each other. In nearly all plants bear- 
ing non-entire leaves, we find that the primary vein system, or strong 
branches from it, the system of channels which conduct the main 
supply of sap to the various portions of the lamina, ends in the teeth 
or lobes,* and, consequently, these parts obtain a greater amount of 
nutrition than the portions immediately around the bases of the serra- 
tures, sinuses, etc. The leaf is but an expansion of a portion of the 
stem, with a greater development of parenchyma; the prosenchymal 
elements are expanded into a reticulum, on which the parenchyma is 
stretched, and these woody parts, bearing the intimate relation to the 
marginal indentations above alluded to, should be given more promi- 
nence ina discussion of this subject than those consisting mostly of 
parenchyma alone, the cells in which the decomposition of carbonic 
acid is effected by the aid of sunlight. Mr. ALLEN has given the 
parenchyma sole importance in his theory, and assigned the vein 
system no function in the production of teeth, lobes, etc. In entire- 
margined leaves we find that the primary veins seldom end in the 
margin, but curve upward, and ultimately become united with one 
another, forming the closed areas known as areoles. 
Mr. ALLEN’s views fail to explain the fact that the leaves of mono- 
cotyledons are almost invariably entire-margined.t Many of these 
plants, and the grasses and sedges in particular, grow closely packed 
together, the leaves of individuals overshadowing those of others and 
* There are exceptions to this general statement, as in the genus Czcu¢a, where the veins end 
in the serratures, and in some species of 7%zfoléum, where they terminate abruptly in the prac- 
tically entire margin. 
+ There are exceptions, as in Yucca, Dasylirion, and Adoe, and other related genera, with 
filamentous or spiny projections from the leaf-margins, and Stratiotes aloides, L., the Euro- 
pean ‘* water soldier.” 
