Heterophylly in Proserpinaca palustris, L. 
BY 
GEORGE P. BURNS, 
University of Michigan. 
With Plate XXXVIII. 
I NDIVIDUALS of the same species growing under different conditions 
often show great variation in form and structure of their organs. 
These variations are, in some cases, very slight, but in others so marked 
that plants showing them have been taken for new species or at least 
varieties. Not only do we find great variety in form and structure of 
organs on separate individuals, but the same individual may form organs 
of very different structure at various stages of its development. These 
variations are in part caused by external conditions. Goebel (i) says : ‘We 
know that external conditions may act as stimuli, but the influence of these 
depends upon the capacity of reaction of the individual plant.’ The 
reactions of plants due to morphogenic stimuli have been studied for the 
most part on the leaves of amphibious plants. These vary in form and 
structure of the leaf. The leaf formed in and remaining in water is quite 
different from the leaf known as the ‘ land-type.’ Many land plants also 
develop two kinds of leaves, and offer a very promising field for experi- 
ment, but so far very little has been done. Only in a few cases do we 
have any experimental knowledge of the stimuli causing the variations. 
In working experimentally along this line two important points must 
be kept in mind. First, ‘ the capacity of reaction of the individual plant ’ 
toward external stimuli is not always the same. Goebel (2) cites numerous 
examples in which the same individual reacts differently in its juvenile and 
adult forms. Secondly, a given reaction is not necessarily the result of 
a single stimulus, but the same reaction may be produced by two or more 
stimuli. However desirable it may be to give a detailed analysis of all the 
possible factors which determine form, and to determine the influence of 
each component upon the protoplasm of the primordial cells, it seems that 
there is little possibility of accomplishing such an end. 
[Annals of Botany, Vol. XVIII. No. LXXII, October, 1904.] 
