40 ARIL OF BIXADS. [BOOK r. 



we have seen in Turnera to what has been described in 

 Piriqueta and Wormskioldia. 



We are led by natural affinities from Turnerads to 

 Bixads, some genera of which possess the organ we are 

 examining. In Bixa, for example, the numerous turbinate 

 seeds of which are each attached to a long umbilical cord, we 

 find a narrow discoid expansion, arising from the latter 

 around the hilum, and which evidently represents a partially 

 developed aril. The umbilical cords adhering to the placenta 

 after the seeds have fallen resemble little nails, the heads of 

 which are formed by the arillary expansion ; the connexion 

 between these cords and the aril cannot be more clear than 

 in this case. 



I have nothing more to add concerning the aril of Bixa ; 

 but on the seeds of this genus there is another excrescence 

 that merits our attention. These seeds are anatropal, with a 

 deep furrow extending on their surface from the hilum to 

 the chalaza, and inclosing the raphe. The latter lying in a 

 superficial pulpy layer of the external integument, only 

 becomes visible a little below the point where the vessels that 

 compose it expand into the chalaza on the inner integument. 

 In this small portion of its length that can be seen, it forms 

 on the seed an elevated, hard, shining line, expanded at its 

 end into a circular, lobed, crustaceous, shiny disc, which is 

 only attached to the seed by its centre, like a flattened button 

 with a very short stem. 



Some physiologists see in the raphe a portion of the umbi- 

 lical cord, which, completely free, when the ovule is ortho- 

 tropal, adheres to the length of the latter, thus making it 

 anatropal ; and they, perhaps, would explain the origin of 

 these two discoid expansions, by looking upon them as two 

 arils arising from the umbilical cord at two different periods ; 

 the first formed, being developed around the hilum when the 

 ovule was orthotropal, the point of its attachment is con- 

 founded with the chalaza; the other, formed at the new 

 point of attachment in the anatropal ovule : this point of 

 attachment is separated from the former and from the cha- 

 laza by the whole length of the raphe. These two expansions 

 would be found on the seed, the first near the chalaza, the 



