186 The Ohio Journal of Science [Vol. XXI, No. 6, 



body. The Bryophytes and Homosporous Pteridophytes may, 

 therefore, be defined as: Those higher plants which normally 

 show no indication of sexual dimorphism in the sporophyte 

 either in respect to structure or function. 



On the other hand, in all of the living heterosporous plants, 

 as intimated above, including the Water-ferns, Quillworts, 

 Selaginellas, Cycads, Ginkgo, Gnetums, Monocotyls, and 

 Dicotyls, there is sexual dimorphism to a greater or less degree 

 and extent in the sporophyte tissues. In the lowest types, this 

 dimorphism does not extend beyond the sporangium and its 

 stalk, but in the extreme diecious species sexual dimorphism 

 may be present to a greater or less degree thruout practically 

 the entire plant. The living heterosporous plants may, there- 

 fore, be defined as: Those plants whose sporophytes always 

 show sexual dimorphism to a greater or less extent, at least in 

 the tissues of the sporangia or sporophylls. 



Because of the appearance of sexual dimorphism in the 

 vegetative tissues of heterosporous sporophytes, it becomes 

 evident that there must be reversals of sexual states in these 

 tissues, either from a neutral state to one or the other sexual 

 state or in some cases from one sexual state to the other or to a 

 neutral state again during the growth of the tissues. The 

 writer has been making observations for several years on a 

 considerable number of monecious species of the type in which 

 the inflorescence is completely staminate in one part and 

 carpellate in the other. In the present paper only such cases 

 are considered which show a general reversal in the flower 

 cluster from the male state to the female or vice versa. A con- 

 siderable number of common species show a general distribution 

 or commingling of staminate and carpellate flowers which 

 might also be studied to advantage. 



In the cases at hand it becomes self-evident that the growing 

 meristem of the inflorescence axis is either in one sexual state 

 and then passes thru a neutral condition during its growth 

 to the opposite sexual state or that it is constantly in a neutral 

 state but the lateral structures derived from it are thrown into 

 the male or female state depending on the functional activity 

 of the cells at the time. The change from carpellate structures 

 in the lower part of the inflorescence to staminate structures 

 above is apparently much more common than the opposite 

 condition, from staminate to carpellate, notwithstanding the 



