PHTLLODY OF THE FLORAL WHOKLS. 303 



divisions of the epidermal layer of the nucellus, one can 

 hardly consider these of themselves as homologous with a 

 true phyllome. But when we find that each of the two sides 

 of an anther cell can develop into a foliaceous structure, as 

 in the case of the Jatropha alluded to above (Fig. 84), we 

 seem to have discovered a power of converting what is 

 originally and simply an epidermal layer into a truly folia- 

 ceous structure. Moreover, this process is not infrequent 

 in certain monstrous states of ovules, so that it would appear 

 that any question of homology is, strictly speaking, out of 

 court in these cases. When the whole of an appendicular 

 organ becomes foliaceous, then, of course, a true case of 

 homology may be recognized. 



Oeigin, Development, and Homologies of Ovules. — Tera- 

 tology, here, I think, assists us greatly. With regard to the 

 structure of an ovule, it first appears as a papilla upon the 

 placenta, the cellular tissue of which, with its epidermal 

 layer, constitutes the first stage. Such may, perhaps, be 

 considered as the rudimentary condition of the funicle alone, 

 as the true ovule is formed at the summit of it. One or 

 more of the apical sub-epidermal cells gradually develop into 

 the nucellus, while the secundine is first formed by tan- 

 gential division of the epidermis commencing at a certain 

 place below the apex ; the primine, if present, subsequently 

 following suit in the same manner.* It is a noticeable fact 

 that while an ovule thus complete is elsewhere general in 

 flowering plants, the Gymnosperms and most orders of the 

 Gamopetalce form remarkable exceptions, as having only one 

 coat to the ovule. In the former of these two groups it is 

 doubtless due to a primitive condition being accompanied 

 by other features showing aflSnities with cryptogams. In 



♦ See paper by Warming, De VOvule, Ann. des Sci. Nat., v. (1877), 

 p. 177. 



