STRUCTURE.] FALSE ARIL OF OPUNTIA. 47 



funicle supporting it ought to leave upon it only a false um- 

 bilical scar j and lastly, the small hole of this envelope which 

 represents the originally large opening of the boat can only 

 be looked upon as a false micropyle. It is on the seed itself, 

 i. e. below the false testa, that the true hilum and micropyle 

 must be looked for. 



Now that we have seen on the seeds of Opuntia an acces- 

 sory envelope, it remains to show the difference between it 

 and a true aril, in order to justify the name of false aril that 

 I have given it. I shall not say that this envelope exists a 

 long time before the expansion of the flower, whilst the aril 

 only appears after impregnation ; the Cytinus has shown us 

 that this character of the aril is not altogether unexception- 

 able, as it was thought to be ; but if it is true that the aril is 

 an appendage of the umbilical cord, and an exterior leaf of 

 the ovulary bud, such an organ cannot be the type of the 

 false testa of Opuntia. 



The latter, notwithstanding its intimate connexion with 

 the funicle, is no more an appendage of it, or a modified leaf, 

 than the flattened branches of Ruscus or of Xylophylla are 

 true leaves. 



It is not formed of a circular or unilateral expansion, like 

 that of the Passion flowers, or of Turnera, but of two thin edges, 

 which, produced from the two sides of the funicle, remind us 

 of productions of a similar nature found on those axes called 

 winged or bordered. Now that we know the origin of the 

 crustaceous envelope which conceals the seed of Opuntia, it 

 will be easy to understand that the portion of the umbilical 

 cord originally curved into a ring is represented by the raised 

 rim found at the contour of this envelope. 



The micropyle is generally looked upon as a canal for im- 

 pregnation, and the supposed existence of a tissue to conduct 

 the fecundating matter is supported by curious and positive 

 facts. When certain ovules, at the time of flowering, are 

 seen invariably to bring their orifice to the same point of 

 the ovary or of the placenta, this point may be properly con- 

 sidered as intended in a special manner to transmit the 

 fecundating agent, and these conclusions have been confirmed 

 by anatomy, which shows the existence of a peculiar tissue 



