FORMS OF COTYLEDONS 9 



leaves, afford, not only to the final leaves, but even to those 

 by which they are immediately followed. 



This contrast between the cotyledons and true leaves is so 

 great that one might almost be pardoned for asking whether 

 they can be brought into actual correlation. 



So far, indeed, are the cotyledons from agreeing with the 

 forms of the leaves, that the difficulty is to find any which 

 have been clearly influenced by them. One species of Ipomcea 

 (/. Pes-caprfe) has both cotyledons and leaves, as the name 

 denotes, somewhat like the foot of a goat ; but the leaves vary 

 considerably, and it is probable that the resemblance may be 

 accidental. A clear case is, however, afforded by the Ona- 

 grarieae, where in (Enothera and some allied genera the form 

 of the mature cotyledons is evidently related to the leaves. 

 Even here, however, the resemblance is confined to a basal 

 portion of the cotyledon which makes its appearance subse- 

 quent to germination, and no trace of it is shown in the coty- 

 ledons themselves when they first appear. 



The forms of the cotyledons in many species have been the 

 subject of special memoirs by Tittniann, Irmisch, Wichura, 

 Winkler, Tscherning, and other botanists ; but they have not 

 given any reasons for the various forms assumed. 



Klebs, indeed, one of the most recent writers on the sub- 

 ject, in his interesting Memoir on Germination, 1 refers to this 

 diversity of form, and expressly says that these differences are 

 an enigma (' Sind gewiss diese Verschiedenheiten in den 

 Blattformen hinsichtlich ihrer biologischen Bedeutung fur die 

 Pflanze ein Kathsel '). He observes, however, that on the 

 whole the forms of cotyledons are much simpler than those of 

 leaves, and he suggests that while in some cases perhaps, like 

 the first leaves, they retain the form which characterised the 

 species in bygone ages, we may rather, as a more generally 

 applicable explanation, apply to them the suggestion of Goebel 

 with reference to stipules, and regard them as simplified by 

 arrest. 2 Another suggestion has been that cotyledons are ' a 

 survival of the universal foliage of deciduous trees in olden 

 geological days, ere time had differentiated them into their 



1 ' Beitrage zur Morphologie und Biologie der Keimung,' Untersiich. Botan. 

 Inst. v. Tubingen, 1884 (Band i. p. 536). * Loc. cit. p. 613. 



