36 ARILLODES. [BOOK i. 



funicle an obstacle to its extension, and ought, therefore, to 

 have a break in its uniformity : but it is here, as it happens, 

 that the expansion is thickest, and it even adheres, along part 

 of its length, to the base of the raphe, so that it looks as if at 

 this point it proceeded from the latter part. To explain this, 

 we must admit there is a congenial junction between the expan- 

 sion and the funicle. I ought, perhaps, to add, in order to 

 clear up doubts, that in Euonymus it is very difficult to see the 

 micropyle, when the ovule is considerably developed, because 

 the false aril is folded round its opening, and so completely 

 hides it : but by carefully pulling away the accessory envelope 

 it is quite clear that it proceeds from the edges of the exostome.* 



We have seen, in the Passionflowers, an expansion deve- 

 loping around the hilum and covering the exostome, by ex- 

 tending over the whole ovule. The same fact, variously 

 modified, is found in other plants. 



In Euonymus, on the contrary, no expansion arises and 

 covers the exostome', but the edges of this opening expanding 

 a little, turn back from the top towards the base of the ovule, 

 and, developing in this direction, form around the latter a 

 sac open next the chalaza. We shall find in other species, 

 a similar expansion of the edges of the exostome produce very 

 various excrescences on the ovule, which have generally been 

 confounded with those of the umbilical cord. 



I have called the expansion of the umbilical cord in 

 Passionflowers an Aril ; but this name will not apply to the 

 envelope which as in Euonymus proceeds from the edges of 

 the exostome. Similar productions are as common as true 

 arils : I shall examine them in detail under the name of 

 false Arils or of Arillodes. 



We may, indeed, say that the greatest number of the parts 

 of a seed as yet considered as arils, will come into the new 

 class. In short, the characters assigned to the true aril have 

 been sufficient to distinguish it from the parts of the pericarp 

 and from the integuments of the seed, whilst they are of no 



* L. C. Treviranus perfectly traced the developments of the false aril of 

 Euonymus latifolius from the time that it half covered the seed ; and he would 

 certainly have arrived at the truth had he traced the progress of this organ from 

 its commencement. 



