182 VEGETABLE ORGANOGRAPHY. 



facilitate its passage and dissemination. But it must be 

 observed here, that this wing resembles several very 

 different organs, or rather that analogous expansions 

 may be developed upon almost all the organs of the 

 fruit: thus, although I am inclined to believe that the 

 greatest number of winged seeds owe this organization 

 to the epidermis, it is nevertheless possible, that some- 

 times the skin itself of the seed may be expanded into a 

 wing ; this seems to take place in the Bignonias with 

 winged seeds ; and I confess that, seeing the adhesion 

 and fineness of certain epidermes, I scarcely know any 

 means (except analogy) to ascertain if the wing of a seed 

 results from its own covering, or from its epidermis. The 

 carpels themselves may expand into wings, as in the soli- 

 tary ones of JYissolia, Sec, or in those united into a single 

 fruit in the Elm ; calyces adherent to the ovary and 

 becoming part of the fruit, form membranous wings, 

 either by the expansion of their limb, as in several 

 Dipsaceas and Compositas, or by the expansion of their 

 angles, as in several Umbelliferse ; and what is remarkable 

 in this degeneration, as well as in the preceding, is that 

 the physiological function of these expansions is ab- 

 solutely the same in every case, whatever be their 

 anatomical origin. The wings always serve for the 

 dissemination either of the seeds properly so called, 

 or of the carpels or fruits which contain but one or 

 two seeds ; for they are hardly ever formed upon poly- 

 spermous fruits. Thus they always serve in the end, 

 wherever they may be placed, to separate the seeds 

 from one another for their natural dissemination. 



I believe that it is also to the presence of a very 

 delicate, but hygroscopic epidermis, that we must 

 attribute a curious phenomenon, viz. — the faculty of 

 certain seeds of absorbing moisture, and of being found, 

 when placed in water or wet earth, surrounded by 



