STRUCTURE.] TRUE AND FALSE ARILS. 33 



it is scarcely visible in the unimpregnated ovary ; aiid it is 

 stated by Brown, that he is not acquainted with any case in 

 which it covers the foramen of the testa before impregnation. 

 The term aril has been misapplied in many cases to the testa, 

 as in Orchids ; and even to a pair of opposite confluent bracts, 

 as in Carex : of these errors, the former arose from imperfect 

 observation, the latter from ignorance of the fundamental 

 principles of Organography. 



The true nature of the aril has been carefully and skilfully 

 investigated by M. Planchon, whose memoir throws so much 

 light upon general structure, that I reproduce it with very 

 little abridgment, although at great length. 



A. Difference between True and False Arils. We will first 

 examine an aril which possesses all the characters assigned to it 

 by Richard ; we will follow its developments, its relations to the 

 ovule and the seed, and we shall be then able to distinguish it 

 from all the organs with which it is at present confounded. 



Let us take the genus Passiflora. On cutting the ovary 

 of a young flowerbud of P. triloba, we find numerous conical 

 tumours, which are rudimentary ovules, arranged on three 

 parietal placentae. In a bud a little more advanced the 

 tumours are longer, their upper part is slightly hooked, and a 

 little below their point two circular rings, close to each other, 

 are found in relief. In these two rings the two integuments 

 of the ovule, as yet scarcely developed, can be distinguished ; 

 the point of each tumour is a small nucleus, the base of 

 which is scarcely covered by its integuments, and the hooked 

 curvature of each of them is a commencement of anatropy. 

 A little later, just before expansion, the anatropy is com- 

 plete ; each ovule is become ovoid ; the two rings are extended 

 into integuments which are still open at the top ; the inner 

 one (secundine, Mirb.) projecting beyond the outer (primine, 

 Mirb.), and the nucleus projecting through the opening of the 

 inner, which, however, conceals its (the nucleus) base. In 

 the ovary of an expanded flower, the top* of the ovule is 



* In this essay, by the top of the ovule is meant the place where the micropyle 

 is found, and where the point of the nucleus ends ; hence it is clear that in 

 anatropal and campylotropal ovules, the top will fee very near the base if we 

 take the latter to mean not the chalaza, but the hilum. 

 VOL. II. D 



