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



plants, still generally in vogue, could be eliminated, more 

 botanists might realize the fact that monecious and diecious 

 species are the extremes and commonly the culmination points 

 of numerous parallel series rather than the first stages of 

 Angiosperm evolution. 



One more example will be given to illustrate the progressive 

 differentiation of larger areas of staminate and carpellate tissues 

 in an ascending phyletic series. In the Cyperacese the least 

 specialized genera have bisporangiate flowers, like the genus 

 Scirpus. Some of the species of this genus have a fairly well 

 developed vestigial perianth of six segments. There are no 

 special structures difficult to interpret. But in the genus, 

 Carex, the perianth is absent and there is present the peculiar 

 perigynium and other unusual structures. Carex is monecious; 

 usually with staminate and carpellate flowers apparently with- 

 out vestiges of the opposite organs. In Carex nardina Fries, the 

 spikelets are all alike containing carpellate flowers below and 

 staminate flowers above. In the highest sedges like Carex 

 lupulina Muhl. the monosporangiate flowers are on separate 

 spikelets, the staminate spikelets above, the carpellate spikelets 

 below. In Carex, therefore, we approach the condition present 

 in Indian corn. 



What is the nature and cause of this progressive change in the 

 area of the tissue involved? In the first case mentioned above, 

 the differentiation takes place in the sporophylls on the same 

 floral axis; in the second case the floral axes produce each but 

 one kind of sporophylls, but the two kinds of flowers are on the 

 same inflorescence axis; in the third case an entire spikelet 

 or group of spikelets is similarly affected. The whole matter 

 can only be interpreted, if at all, by a study of the evolutionary 

 series of expressions in related species. Isolated studies do 

 not give a true picture; in fact do not present the problem. 

 But in no study could the phenomena of segregating or associ- 

 ating chromosomes be involved but the much more difficult 

 problem of changing hereditary expressions and states in a 

 common vegetative tissue. 



As an example of the changes of morphological expression 

 that take place in a growing bud, an ordinary grass may be 

 considered, like Bromus secalinus L. The grasses are derived 

 from plants whose buds produced three spirals of leaves in the 

 vegetative parts as well as in the flower, the ancestral flower 



