LABURNUM, BROOM, AND GORSE 



vetches the terminal leaflets are usually converted 

 into tendrils, to assist these weak-stemmed plants 

 in reaching the sunlight. Just in the same manner, 

 too, the leaves of the laburnum, broom, and gorse 

 have been modified from the type of their common 

 ancestor best to serve their individual require- 

 ments. 



Of the three plants in question, the laburnum 

 has probably seen fewest vicissitudes in the course 

 of its evolution. Its stout trunk, large leaflets, and 

 long pendent racemes of flowers, all indicate that 

 it has not been harassed very considerably. Grow- 

 ing as it does on the mountain slopes of France, 

 Switzerland, and Southern Germany, and often so 

 placed as to be inaccesible to browsing animals, it 

 has apparently been able to develop its structure 

 and spread out its leaves and flowers without much 

 interference. 



Its leaves are produced in little clusters ar- 

 ranged along the branches ; the larger ones have 

 long stalks, which allow them to extend beyond 

 the smaller ones. It follows, therefore, that, 

 if the longer leaves possessed the pinnate leaflets 

 characteristic of its family, the smaller leaves 

 would be covered by them. In the present ar- 

 rangement, however, the smaller leaves fill in 

 the intervening spaces, and so all the leaves get 

 exposed to the sunlight. Also, by clustering the 

 leaves together and exposing them to the sun- 

 light on the upper sides of the branches, it allows 

 a clear way beneath in which to suspend the 

 racemes of flowers (see Fig. 64, Plate 43). 



87 



