NATURE'S WOODCRAFT: A CHAPTER ON STEMS 225 



for the thought to a still earlier botanist. " In open tracts of country, 

 the very circumstance of the sterility of the soil must prevent the pro- 

 duction of many plants ; and of those which grow, few will be enabled 

 to perfect many seeds. It is necessary, therefore, to protect such as are 

 produced from extermination by the browsing of cattle, otherwise not 

 only would the progeny be cancelled, but also the present generation be 

 cut off. And what more beautiful and simple expedient 

 could have been devised than ordaining that the very 

 barrenness of the soil, which precludes the abundant 

 generation by seed, should at the very same time, and by 

 the very same means, render the abortive buds (abortive 

 for the production of fruit) a defensive armour to protect 

 the individual plant, and to guard the scantier crop which 

 the half-starved stem can bear ? That such an armature is 

 produced by the abortion or partial development of buds 

 and branches, there is abundant proof. For not only are 

 thorns found in every stage, varying from their simple 

 dormant or winter state, when, if opened, they contain 

 the rudiments of leaves, through leaf-bearing spines to 

 rigid thorns on the one hand, or leaf-clad branches on 

 the other ; but the very organs, i.e. buds, which, when the 

 plant is half-starved, are partly developed as spines, and 

 partly only as branches, become, when an abundant 

 supply of nourishment is provided, altogether leafy 

 branches : the buds have all been wholly developed, none 

 have degenerated into thorns, and the plant is tamed. 

 The Common Rest-harrow (Ononis arvensis) is a familiar 

 example immediately in point, for of it there are two 

 well-known varieties called 0. spinosa and 0. inermis, from 

 the circumstance of this being smooth and destitute of 

 thorns, while that is covered with them. These two 

 varieties I have often seen growing together on the same 

 heath ; the one well-clad with its offensive and defensive 

 arms, and furnished with few leaves to tempt the appe- 

 tite of cattle ; the others, upon or near to which a care- 

 less cow had dropped a profusion of manure, replete with A portion o the culm 

 leaves and blossoms, but wholly destitute of thorns, and showi eaed Se nodes tbick " 

 just in such a state as to furnish an agreeable repast to 

 the animal by which it had been so richly endowed." 



The wonderful way in which stems seem able to adapt themselves to 

 circumstances, terrene, climatic, and otherwise, is even more strikingly 

 illustrated in the tropical Spurges (Euphorbiaceae). These adopt the forms 

 and habits of the Cactese, an order of plants from which they are widely 

 separated, developing the same succulent tissue (a provision against rainless 

 18 



FIG. 280. BAM- 

 BOO. 



