STRUCTURE.] ARILLODE OF EUONYMUS. 35 



them to the study of a ripe seed, as is proved by the following 

 remarkable instance. 



Nothing is more like the aril of Passionflowers than the 

 so-called envelope found on the seeds of Euonymus ; it is a suc- 

 culent, loose, folded sac covering the seed in a greater or less 

 degree, which does not adhere to it except round the hilum 

 and at the origin of the raphe ; the sac is, in short, more or 

 less open next the chalaza. Let us add that this envelope is 

 not formed until after fecundation, a ad we shall have an appa- 

 rent identity between this organ and the aril of Passionflowers. 

 We shall, however, see that this identity is apparent only. 



Let us take Euonymus latifolius ; in its ovary we find two 

 globular ovules suspended parallel to one another at the 

 inner angle of each cell a little below its top. About the 

 time of expansion they become completely anatropal ; their 

 outer integument covers the inner one and the nucleus ; the 

 raphe, which is prominent, occupies in each of them the side 

 opposite the periphery of the ovary, and the micropyle, on 

 the contrary, is between the point of attachment and the 

 interior angle of the cell at the top of the ovule. 



The umbilical cord is white, as the ovule also is next the 

 hilum, but at its other end it is of a rosy colour which 

 gradually extends over the whole seed. For some time after 

 the fall of the petals and stamens the ovule grows, but does 

 not undergo any external change. The edge of the exostome, 

 however, soon thickens, and looks like a rim round its narrow 

 opening, reminding one by its origin, its nature, and even a 

 little by its form of the caruncula of Spurgeworts. This rim, 

 however, grows, expands into a membrane at its edge, and, 

 turning back next the base of the ovule, becomes a hemi- 

 spherical cap which partly covers the latter, leaving however, 

 at its origin, the micropyle uncovered. This expansion, 

 lastly, increases its surface, draws its opening nearer and 

 nearer the chalaza, and forms around the seed the succulent 

 bag hitherto described as an aril. 



When I stated that this sac proceeded solely from the 

 exostome, I have, perhaps, sacrificed exactness to clearness. 

 As the hilum is very near the micropyle, the arilliform expan- 

 sion starting from the edges of the latter would find the 



