HOW PLANTS EAT. 5l 



member of the great group of " papilionaceous," 

 or butterfly-blossomed, plants, which includes 

 the pea, the bean, the laburnum, the clover, and 

 many other familiar trees, shrubs, and climbers. 

 It is descended more immediately from a special 

 set of trefoil-leaved peaflowers, like the clovers 

 and lucernes ; but, owing to its chosen home on 

 open uplands, almost all its upper leaves have 

 been transformed for purposes of defence into 

 sharp, spine-like prickles. Indeed, the leaves 

 and branches are both prickly together, so that 

 it is difficult at first sight to discriminate between 

 them. But if you take a seedling gorse plant 

 you will find that in its early stages it still pro- 

 duces trefoil leaves, like its clover-like ancestors; 

 and- these leaves are almost exactly similar to 

 those of the common genista so much cultivated 

 in hot-houses. As the plant grows, however, 

 the treff^il leaves gradually give place to long 

 and narrow blades, and these in turn to prickly 

 spines, like the adult gorse-leaves. Hence we 

 are justified in believing that the ancestors of 

 gorse were once genistas, bearing trefoil leaves ; 

 and that later, through the action of natural 

 selection, the prickliest among them survived, 

 till they acquired their existing spiny foliage. 

 In every case, indeed, young plants tend to re- 

 semble their earlier ancestors, and only as they 

 grow up acquire their later and more special 

 characteristics. 



And now I must add one word about the 

 origin of leaves in general. Very simple plants, 

 we saw, consist of a single cell, which is not 



