46 FALSE ARIL OF OPTJNTIA. [BOOK i. 



and because, being completely developed before the expansion 

 of the flower, it has always been described, not as an aril, 

 but as a true testa. How can one, indeed, avoid taking for a 

 proper integument the exterior envelope of the seeds of 

 Opuntia, a hard, thick, reniform stone bordered by an elevated 

 rim, and presenting no trace of any opening even when free 

 from the pulp with which it is covered ? It is, however, this 

 very stone that I call a false aril or false testa, the origin and 

 nature of which must be looked for in the early development 

 of the ovules. 



Those of Opuntia vulgaris, composed in a very young 

 flower-bud of an ovoid nucleus and of two open integu- 

 ments, end in thick funicles, with which they are perfectly 

 continuous. Each of the latter, originally nearly straight, 

 is gradually bent into a semicircle, and approaching at. its 

 base the point of the nucleus, forms a complete ring with 

 the ovule. In that half of the ring which is lowest with 

 respect to the ovule, arise, on the sides of the umbilical cord 

 and at some distance from its base, two rather concave mem- 

 branous expansions, which originate next the ovule and soon 

 conceal the empty space comprised in the turn of the ring. 

 The funicle and its two expansions then represent a sort of 

 boat with a very large opening, and the cavity of which imper- 

 fectly conceals the ovule, which gets deeper and deeper into 

 it. The latter soon disappears ; the diameter of the opening 

 remains the same, but seems to diminish in consequence of 

 the very considerable growth of the ovule ; and the side of 

 the boat, distended by the young seed, soon forms for it a 

 complete envelope. It is here that all the transformations 

 of the ovule take place; from being orthotroparit becomes 

 amphitropal, and changes, in this conversion, the direction 

 of its micropyle, which, instead of being opposite the base of 

 the funicle, is turned to the opposite side. Lastly, the ac- 

 cessory envelope of which we have been speaking, becoming 

 thick and hard like a stone, and being covered on its outside 

 with plenty of pulp, plays the part of a crustaceous testa with 

 respect to the seed, and protects its thin proper integuments. 

 But it is clear from what has now been stated, that this stone 

 is nothing but a false testa; the cylindrical portion of the 



