128 SPINES AND THORNS [CH. 



in the axil of a leaf, or, what is the same thing, from the 

 upper edge of the leaf-scar. 



lu this way the observer sees at once, from direct ob- 

 servation, that the spines on the Robinia, Gooseberry and 

 Barberry cannot possibly be true thorns, as above defined, 

 because they neither originate from the leaf-axils nor 

 themselves bear buds or leaf-scars, &c. On the other 

 hand the spines of Rhamnus catharticus, Hippophae, 

 Mespiliis, Blackthorn and Hawthorn are obviously true 

 thorns, because they either terminate a twig bearing 

 leaves and buds, or they arise in the axils of the leaves 

 and themselves bear such organs. That the latter are 

 merely dwarf-shoots hardened and sharpened at the tip is 

 clearly seen in the Pear, where every gradation between 

 short stumpy blunt dwarf-shoots and sharp thorns is to 

 be found. 



In Genista anglica and the Gorse the same is true, but 

 somewhat more careful observation is needed to establish 

 the fact when the leaves are absent. 



What, then, is the morphological nature of the other 

 spines mentioned above ? 



In Robinia there is no escaping the fact that the 

 spines originate right and left from the base of the petiole 

 of the leaf: from that part which is left behind on the 

 twig after the leaf has fallen, and in the axil of which we 

 find the buds. And similarly in the Gooseberry, the 

 spines obviously spring from the bases of the leaves, 

 which bear buds in their axils. They are therefore repre- 

 sentatives of something belonging to the leaf-base or to 

 the leaf-cushion (pulvinus) found at the base of the 

 petiole. Careful study of their youngest stages, and com- 

 parison with other forms, have shown that in Robinia the 

 spines represent the stipules found in other closely allied 

 plants ; while in the Gooseberry they arise from the 



