52 



ON SEEDLINGS 



the lobes of the cotyledons draw themselves out one by one. In 

 Opuntia basilaris, again, which differs from 0. Labourtiana in 

 having narrow cotyledons, the seed-coats are similarly carried 

 up, and the cotyledons free themselves by divergence. In this 

 species, also, it is interesting that one or both cotyledons are 

 often bifid. Is it possible that the multiplicity of the cotyle- 

 dons in Conifers (fig. 98) can be due to the same cause ? 



In Ephedra there is a special membrane, which remains 

 attached to the root, and thus prevents the testa from being 

 carried up on the tips of the cotyledons. 



The common Cress (Lepidium sativum) (fig. 4), to which I 

 have already referred, is a very interesting case, for while in 



FIG. 99. Section of seed of Lepi- 

 dium graminifolium, x 15. 



FIG. 98. Seedling of Finns 

 rigida, x 2. 



Fm. 100. Section of seed of 

 L. sativum, x 16. 



the other species, at any rate in the other English species, of 

 the genus the cotyledons are entire, in Lepidium sativum, on 

 the contrary, each possesses two long, narrow lateral lobes. 



Fig. 99 represents a section through the seed of L. gramini- 

 folium, which may be taken as representing the ordinary 

 arrangement in the genus. The seeds, conforming to the 

 shape of the capsule, are somewhat triangular, with the radicle 

 in the narrow end. The embryo occupies the whole of the 

 seed, there being no endosperm. In L. sativum (fig. 100) the 

 seed is of the same form, but nearly twice as large, and if, 

 therefore, the cotyledons were to occupy the whole additional 



