134 ON SEEDLINGS 



lower ones rounded, indehiscent, and transversely multi- 

 locular. 



Geococcus buries its pods in the ground. 



The Order presents a vast amount of variation in the form 

 of the fruit, seed, and embryo. For purposes of classifica- 

 tion of the genera, it is above all things necessary to consider 

 the form and characters of the fruit ; though these do not 

 invariably indicate the true lines of natural affinity, as for 

 instance in the case of Raphanus and others amongst the 

 Baphaneee, and Crambe, Rapistrum, and others amongst the 

 Cakilineaa, which are obviously closely allied to the Brassiceae. 



The Order may be conveniently divided into five groups 

 according to the form and folding of the embryo, excluding 

 some aberrant species which may be dealt with separately. 

 It must be admitted, however, that the form of the embryo 

 alone will not in all cases indicate the true lines of natural 

 affinity, although it offers a convenient means of grouping 

 the seeds. The latter are exceedingly variable in mere out- 

 line, being flat, compressed, ovoid, oblong, linear, globular, 

 or winged; but none of these characters are so constant as are 

 the various forms of the embryo. The latter may be briefly 

 described as having the cotyledons accumbent, incumbent, 

 conduplicate, transversely biplicate, and circinately convolute, 

 while in the aberrant forms the cotyledons are sometimes 

 deeply divided. 



Taking the Wallflower (Cheiranthus Cheiri) (fig. 158) to 

 represent embryos having accumbent cotyledons, we find that 

 the seed is oblong-oval, much compressed laterally, with the 

 edges produced all round into a thin membranous wing. The 

 embryo is flat with ovate, obtuse, entire cotyledons, and the 

 terete, slightly curved radicle is laid against the edges of the 

 closely adpressed seed-leaves. If the double seed-coat is removed 

 from one side of the seed, the edges of the petioles are seen, in 

 some cases at least, as if the embryo had originated with the 

 cotyledons in the narrow plane of the seed and the seed-leaves 

 had afterwards become twisted round to accommodate them- 

 selves in the broader plane during the process of growth. 



Embryos with accumbent cotyledons prevail throughout 

 the Arabideae, Alyssineae, Thlaspidese, and in five genera at 



