ONLY ONE CATEGORY OF LEAVES 187 



This precocity, however, does not alter its nature as an early foliage leaf, 

 bearing essentially the same relation as others do to the sporophylls, and 

 to the relative axis. 



In support of this conclusion it may be noted that, according to Prantl, 

 even the primordial leaves of Lygodium subalatum are sporophylls, so 

 that sterile leaves do not exist at all in that species. 1 No more complete 

 demonstration is possible than this of the correctness of the conclusion 

 that the cotyledon is the equivalent of the foliage leaf, and of the sporo- 

 phyll. The position at which we arrive is then this : that foliage leaves 

 are sterilised sporophylls, and the protophylls or cotyledonary leaves are 

 further modifications of the same type. In fact, all those parts which 

 are commonly styled " leaves " on the Pteridophyte plant belong to the 

 same category, but differentiated to meet special needs. 



1 Schizaeaceen, p. 14. 



