42 



ON SEEDLINGS 



The terminal lobe is the original cotyledon, and the basal 

 portion is altogether subsequent growth, which, moreover, to 

 some extent, assumes the character of the true leaf. I shall 

 presently refer to this interesting group in more detail. 



The case of Petiveria octandra (fig. 66) has been already 

 described. 



EMABGINATE COTYLEDONS. 



In a great many species the cotyledons are emarginate, and 

 even in some more or less deeply bifid. No explanation of this 

 has, so far as I know, yet been offered. It is, in fact, as I shall 

 hope to show, by no means always due to the same cause. 



* r 



FIG. 82. Longitudinal and transverse sections 

 of seed of Impatiens parviflora x 10 : PI, 

 plumule. 



FIG. 88. Longitudinal section 

 of Poterium Sanguisorba, 

 x 9 : ct, calyx-tube ; a, achene ; 

 re, receptacle. 



One of the simplest cases is that of the Oak, where the 

 thick fleshy embryo occupies the whole of the seed. The 

 chalaza is situated at the centre of one end, at the extremity 

 of the cotyledons, and the walls of the seed being at that 

 point somewhat thickened, the cotyledons are slightly pressed 

 in. The same explanation applies to various other species, 

 as, for instance, to the Impatiens (figs. 12 and 82), Pote- 

 rium (figs. 42 and 83), Cuphea (fig. 84), and Nettle (Urticd) 

 (fig. 85). 



In Helianthus Cucumis the seed itself is slightly notched 



