ON THE SUBSIDIARY CJSES OF BTIP! LES L89 



and Hooker ('Genera Plant.,' i. p. 625) include it in 

 Uosa\ as does also Focke, who, however, considers it to 

 be a distinct subgenus, characterised by its simple ex- 

 stipulate leaf. It is a low busji found in the deserts of 

 Persia and Turkestan. 



The Beech, Hornbeam, Lime, Oak, and many other 

 trees, afford instances where the stipules, though attain- 

 ing some size, are caducous, more or less scarious, and 

 do not serve for protection nor for assimilation. 



Stipules converted into Spines 



In some species, belonging to very different families, 

 the stipules, or some of them, are converted into spines, 

 as, for instance, in some Acacias, Mimosas, &c. 



In Bobinia (E. Psendacacia, commonly called the 

 Acacia) the winter-bud is protected by three short, 

 brown, triangular scales. On the young growing 

 shoots the stipules are linear, subulate, and hairy. 

 Ultimately they thicken and become woody, brown, 

 persistent spines. They are less developed on the 

 upper branches, where the need for protection is not so 

 great. Zizyphus Jujuba is another case in which the 

 stipules are spiny. Here also the two stipules are 

 unequal, that on the upper side of the shoot being 

 the longer. 



Gappcvris also (C. spinosa) has two spines at the 

 base of each leaf. As Colomb (19, 67) admits, they 



