42 ARIL OF NYMPILEA ; [BOOK i. 



always proceeds from this point. We ought, then, to consider 

 in Bixa only that discoid expansion which is around the point 

 of attachment as an aril, while the opposite expansion must 

 be looked upon only as an appendage of the integument. 



But to return to my subject, from which I have, perhaps, 

 wandered too far, I find the aril, with all its characters, in the 

 genus Nymphsea. The anatropal ovoid seeds of Nymphaea 

 cserulea are entirely covered with a white membranous enve- 

 lope, which is inserted round the hilum ; and being applied, 

 but not adhering to the entire surface of the testa, has but a 

 small opening next the chalaza. Below this envelope, which 

 is a true arillary sac, we find on the side of the point of 

 attachment a very distinct micropyle ; this sac has, therefore, 

 been wrongly described as an epidermis of the proper integu- 

 ment. This error would be dispelled by an examination of 

 the seed ; but we find still stronger characters in the develop- 

 ment of the ovules of another species of the same genus. If the 

 ovary of Nymphsea alba is opened a little before the expan- 

 sion of the flower, on no one of its numerous anatropal ovules 

 is any trace of an accessory envelope to be found ; their 

 exostome is also quite open to view. A simple rim found on 

 the funicle immediately above the hilum, evidently indicates 

 the origin of the membrane which, in Nymphsea cserulea, 

 entirely conceals the seeds ; but at a later period, in the same 

 ovules, the rim is extended into a hemispherical cap, crowning 

 their summit and afterwards covering the entire seed. I have 

 not been able myself to observe this transitory state of the 

 aril of Nymphsea alba ; but I depend for the accuracy of my 

 statement on De Mirbel's excellent observations on the ovule; 

 than which I can have no better authority. 



We might expect to find some sort of aril on the seeds of 

 Nuphar, which is very nearly allied to Nymphsea ; however, 

 there is none ; the seeds of Nuphar lutea, for example, have 

 no trace of any accessory membrane, either on their crusta- 

 ceous integument, or on their micropyle, which is very visible. 

 I need not state that this envelope does not exist on the 

 seeds of Neluuibium. 



The amphitropal, lenticular seeds of Chamissoa nodiflora 

 (Nat. Ord. Amaranths) have at their base a shallow 



