﻿Assimilating Tissue in Sporophytes. 29" 



garding the relation of the perianth to the other appendages the 

 ready metamorphosis of the stamens of the Rosaceae, Nymphea- 

 ceae and Ranunculaceae to petaloid structures present interesting 

 examples that indicate that the corolla, at least, may have resulted 

 r om the sterilization of sporogenous tissue, and this seems the more 

 probable when we associate the reduction of the essential organs 

 of the flower with the advent of the perianth. The question may 

 properly be asked to what category do the assimilatory appendages 

 of the mosses belong. Physiologically they are leaves and their 

 origin, though on an antithetic generation, is doubtless due to 

 eruptions of the shoot brought about possibly, in some cases, 

 through food accumulations which become a hereditary character 

 in some plants and a fruitful source of variation, and especially has 

 the stimulus of light been a potent factor in the development of 

 assimilatory organs. As indicated above, a similar cause may 

 have given rise to the leaf of the vascular plants, as is possibly 

 true among the Filicinae, but the reduced leaf character of the 

 Equisetinae and Lycopodinae, together with the abortion of the 

 sporangia, certainly suggests their derivation from sterilized sporo- 

 phyls. Schwendener's conception of a leaf as a lateral appendage 

 of the shoot that differs from it in character rather than grade or 

 rank is an excellent definition, but the failure to regard the homol- 

 ogies and phylogeny of these lateral organs has led to the serious 

 misconceptions regarding morphologies so commonly recurring 

 in text-books of botany. 



