39 2 ON THE GEHIMNATION 



and afterwards, in the progress of vegetation, by 

 the point of the first leaf, (PI. XIII. fig. 2.) which 

 previously appears of a green colour through their 

 substance. M. Gaertner names the sheath " va- 

 " gina cotyledonia" (as he observed only one) ; 

 but in reality the sheaths have no analogy with 

 the scutellum or Cotyledon : every one of the se- 

 minal bulbs having one proper to itself, whereas 

 there is but a single Cotyledon. On the other 

 hand, these sheaths have the closest analogy with 

 the involucra of the buds of the stem, with this 

 difference, however, that the latter (in such ge- 

 nera as I have examined, as Avena, Arundo, and 

 Poa,) are open towards the point; whereas the 

 sheaths of the seminal bulbs are entire, until 

 pierced by the first leaf. 



THE SEMINAL TUBER. 



M. Mirbel, in a memoir read before the Insti- 

 tute of France on the Germination of the Gra- 

 minese, notices this part, without however ascer- 

 taining its use. " La plumule et la radiculc sont 

 " unies par l'intermediaire d'un nceud charnu ; ce 

 " renflement se prolonge a sa base en un petite 

 " sac, dans lequel est renferme la radicule." 

 This " noeud charnu," however, as I have already 



* Amahs du Museum, t. xiii. 2d & 3d cahiers, 

 7 annee. M. Gaertner also indistinctly refers this or- 

 gan to the " indivisse cotyledones — u nihil aliud sunt 

 84 quzm zj>se scapus embryonis^—YT&i* chap. xlix. 



