314 The Ohio Naturalist. [Vol. Ill, No. 1, 



OHIO PLANTS WITH DISSECTED LEAVES. 



Harriet G. Burr. 



An ordinary ])lant 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 possihle without causing injury to 

 their structure. Under 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 oi 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. 



Below are shown lists of the more typical Ohio i)lants 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 Bidciis Bcckii 

 or Water Marifjold. The submerged leaves are verv finelv 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 necessarilv 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 

 ])lants are crowded together, as they are sometimes along our 

 roadsides, a simple entire leaf would shade those beneath it, 

 whereas compound and dissected leaves alk)\v 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 



