3*4 
The Ohio Naturalist. 
[Vol.III, No. 1, 
OHIO PLANTS WITH DISSECTED LEAVES. 
Harriet G. Burr. 
An ordinary plant is dependent upon light for its nutrition ; 
and, since the leaf is the organ in which the food is mainly manu- 
factured. it follows that the leaves are arranged in such a way as 
to give them as much light as possible without causing injury to 
their structure. Linder ordinary circumstances they have an ex- 
panded blade which presents a large amount of surface in propor- 
tion to the mass. Whenever this is not the case we look for some- 
thing in the environment to explain the departure from the usual 
condition. 
There are plants which, typically, have leaves of a certain 
form, but which, when grown in a different situation, produce 
leaves of an entirely different character. Plants which grow in 
very dry regions and also in moister regions have a typical form 
of leaf for each condition. The same is true of those plants which 
grow sometimes submerged in water and sometimes on dry land. 
In the case of many plants which grow with a part submerged 
and a part above water, each will have its own form of leaf. Sub- 
merged plants invariably produce the most finely dissected leaves ; 
plants which grow in crowded or in very dry situations also usually 
produce much-divided leaves. 
P>elow are shown lists of the more typical Ohio plants which 
have leaves of this kind. The first list comprises those which grow 
in water; the second, those which grow in dry land, whether in 
dry or moist soil. 
One of the most striking of the water plants is Bidens Bcckii 
or Water Marigold. The submerged leaves are very finely dis- 
sected, the plant blooms above water, and the upper leaves are 
above water ; all these latter leaves are simple and undivided. The 
second list is necessarily more heterogeneous than the first, in- 
cluding plants found in moist, rich woods, in waste places, and 
on roadsides, in dry, hot situations, and so forth. 
The cause ordinarily given for the dissected leaf under these 
conditions is the adaptation to secure as much light as possible 
for those which grow in crowded situations, and to reduce trans- 
piration as much as possible for those in dry conditions. Where 
plants are crowded together, as they are sometimes along our 
roadsides, a simple entire leaf would shade those beneath it, 
whereas compound and dissected leaves allow the light to sift 
through them and so reach those below. 
Finely dissected leaves are much better adapted to a water 
medium than leaves with undivided or with large blades would be; 
and it is this adaptation, together with the response to diminished 
