38 The Nature and, Origin of Stipules. 



As the other portions of the primitive leaf have been so won- 

 derfuiry modified in the course of their development and altered 

 from their original condition, so the freed lateral portions to 

 which we may now apply the term stipules have not retained their 

 primitive proportions in adult leaves nor the identit} r of all their 

 parts. Bat as the central basal portion has often almost wholly 

 degenerated, the same thing has happened to the basal parts of 

 the lateral portions. The parallel degeneration of the two por- 

 tions has brought the stipules into closer and closer apparent re- 

 lation to the stem, so much so as to lead to the enquiry whether 

 they are not accessory leaves and to suggest their origin from the 

 reduction or lack of development of a portion of the leaves as in 

 Selaginella and their subsequent association in close relation to 

 the larger ones, but in all my investigation I have not found 

 the slightest evidence in support of this theory. The degener- 

 ation of the stipules may continue until they become vesti- 

 gial or finally disappear altogether. This is evidently the case in 

 those families of plants a few species only of which still possess 

 stipules, as for example the Caprifoliacere. 



But opposed to the basal degeneration of stipules, there has 

 very commonly been a longitudinal development corresponding 

 to that l>3 r which the lamina has been evolved. This has resulted 

 in the adaptation of the stipules to the peculiar requirements of 

 each genus and species. Often in this secondary development 

 they remain membranous, serving the protective function only, 

 and when free are early deciduous. But in numerous cases they 

 have acquired the assimilative function also, developing abundant 

 chlorophyll and sometimes, as in the pea (Pisum sativium L.), be- 

 coming of equal assimilative importance with the lamina. In 

 Lathy rus Aphaca L., they even replace it almost entirely. 



Among all these varying forms we should expect to find closer 

 similarities in those plant groups of nearer relationship as we do 

 in floral structures, and conversely these similarities of foliar de- 

 velopment should also point to relationship, due allowance being 

 made for parallel development in adaptation to similar environ- 

 ment and for secondary functional modifications which find mor- 

 phological expression. Also in types more recently evolved and 

 more highly differentiated wide divergence from the typical mode 

 of development may be looked for. The Caprifoliacese, before 

 mentioned, are of such a type, with stipules usually wholly aborted; 



