102 The Ohio Journal of Science [Vol. XVIII, No. 4, 



related to the environment, the submerged leaves being dis- 

 sected and the aerial leaves of the ordinary broad type, char- 

 acteristic of closely related genera and species. In Lepidium 

 perfoliatum L. there is just as abrupt and striking a change 

 at the middle of the stem although there is no change in the 

 surrounding medium. The lower leaves are finely dissected, 

 while the upper are entire, oval in shape, and deeply clasping. 



These dimorphisms are changes of states or expressions of 

 hereditary units in the common tissue of a growing shoot. 

 It is plain that they have to do with activity and latency rather 

 than with the presence and absence or the shifting of hereditary 

 units. This fact is to be kept in mind further on in the dis- 

 cussion of analogous sexual phenomena. Similar dimorphisms, 

 although usually not so abrupt, are, of course, very general 

 in great numbers of rosette plants. There are also cases where 

 there is an abrupt, new development of shape, structure, and 

 often color in the leaves just below the inflorescence. This type 

 of vegetative dimorphism is especially common in the Euphor- 

 biace^. 



Among the fungi and many other organisms another type 

 of dimorphism is common, which often involves not only the 

 reproductive cells, but also the surrounding hyphae. In the 

 Ascomycetae there is generally a decided difference between 

 the conidial and ascus stages. These differences appear in 

 different branches of an individual mycelium. The difference 

 in sexual and nonsexual reproductive parts of such fungi 

 corresponds to the vegetative dimorphisms mentioned above in 

 that the phenomena are not associated with shiftings of the 

 chromosomes. In some cases they are produced at rather 

 definite stages of the life cycle, in others the change of expression 

 depends on the environment. 



Now what is meant by sexuality? In its simplest form it 

 is a ph^^siological difference expressed only in the developing 

 sexual cells. As we go up the scale of plant complexity, we note 

 that more and more of the tissues are involved until finally 

 in the extreme forms the entire organism seems to be affected. 

 From the evidence to be presented it must become apparent 

 that in at least the vast majority of cases, and probably in all, 

 the sexual condition is simply a state of the living substance 

 which may continue for a greater or less length of time before 

 a neutral state or the opposite sex condition is set up. 



