204 MISSOURI BOTANICAL GARDEN 



compared with that of typical forms in the same family 

 and with the typical and aberrant forms in apically dehis- 

 cent groups. 



much 



of reg 





Systematic Relationship and Morphological Charac- 

 teristics of Apically Dehiscent Forms. 



Dehiscence by pores may be characteristic of families, 

 genera or species. In the Rapateaceae, Tremandraccae, 

 and, with the exception of comparatively few genera and 



larger Melastomataceae, dehiscence 

 occurrence. It may be found, how- 

 ever, in only a few of the genera, as in Solanum of the Sol- 

 anaceae, Cassia of the Caesalpinioideae, Cheiranthera of 

 the Pittosporaceae and other examples which might be ad- 

 vanced. Probably the best illustration is the monotypic 

 Fissicahjx, the single apically dehiscent genus among over 

 300 belonging to the Papilionatae. Only certain species 

 of a genus, again, may have anthers with pores instead of 

 longitudinal slits. The two Brazilian, and possibly two 

 Indian species, of the 400 assigned to Begonia may be 

 recalled in this connection, as may also three species 

 forming the section Leucoxylum of Diospyros. The api- 

 cally dehiscent habit has unquestionably been assumed in- 

 dependently by many unrelated genera and doubtless at 



various times. The regular occurrence of this method of 

 dehiscence in several large groups indicates that in these 

 cases the habit of dehiscence is much older, perhaps as old 

 as the group itself. There is much to suggest that the 

 apically dehiscent forms of the Solanum-Cassia and Melas- 

 tomataceous types have originated from actinomorphic 

 forms with more or less patent perianth. Evidences of 

 exceptions to this generalization are, however, to bo seen 

 in several cases and in view of our almost complete igno- 

 rance of primitive floral types we can hardly venture to 

 hazard any statements as to the phylogeny of these forms. 



While evidence is too mf»Aat>r fcn nApmif r,f an™ ,.,,„,. i,, 





