38 MORPHOLOGY OF SPECIES 



not protect plants against drought, neither can we regard their 

 production in their present perfect form as a mere accident due to 

 the larger development of the woody character of a plant. It 

 seems to me that, at present at any rate, the only explanation of 

 spines is that they are a protection against animals ; and this has 

 been brought about by natural selection, those seedlings which 

 survived being just those best able to protect themselves from 

 animals. In other words, the reduction of the succulent tissues, 

 the hardening of the mechanical elements, and a consequent ten- 

 dency to spininess, although due primarily to variabihty and 

 environment, have been gradually perfected and made permanent 

 by natural selection. It is quite true, nevertheless, that a favour- 

 able environment tends to reduce the spiny character of a plant ; 

 but it would probably take many years of very careful artificial 

 selection before the Furze plant could be brought back again to 

 the ancestral form possessing only trifoliate and non-spinescent 

 leaves. 



The development of the Furze seedling offers many interest- 

 ing features. The seed germinates in the normal way by sending 

 down a primary tap-root, first of all, into the soil, and a plumule 

 with two fleshy cotyledons upwards into the air. The cotyledons 

 are forced through the soil by the arching of the hypocotyl (Figs. 

 I to 7). They are thick and fleshy, white or light green in colour 

 on the under surface, dark green above, oval in shape, and with 

 no hairs. In a normal seedUng the cotyledons are succeeded by 

 one or two pairs of trifoliate leaves, covered with hairs (Figs. 7 

 and 8). These are generally curved upwards at the margins, and 

 thus grooved or concave on the upper surface. They are thick 

 and shiny and of a dark green colour. The trifoliate leaves are 

 succeeded by several pairs of spathulate leaves, broader at the top 

 than at the base ; they are both described by Lubbock as petio- 

 late. The arrangement of these first leaves varies. They may be 

 alternate and spiral, but are usually opposite to each other and in 

 pairs. The spathulate leaves are succeeded by leaves which gra- 

 dually become less and less broad at the apex, until finally we get 

 a narrow-pointed leaf tapering from tht base upwards (Fig. 10). 

 At the same time, a spine, which is already present in a rudiment- 

 ary condition in ihc trifoliate leaf, becomes more and more deve- 



