106 



MOKPHOLOGY 



and one cannot determine why they came without know- 

 ing ranch of the genealogy of the plant. In some 

 cases they seem to be the result of 

 the contraction of the plant -body, 

 as in the cacti and other desert 

 plants; and they may then serve a 

 purpose in lessening transpiration. 

 It is a common notion that spines and 

 prickles exist for the purpose of keep- 

 ing enemies away, and that hairs 

 keep the plant warm, but these ideas 

 usually lack scientific accuracy. Even 

 if spines do keep away browsing ani- 

 mals in any plant, it is quite another 



question Why the Spines Came to be. 159. The diminishing leaves 



To answer the question what spines of boneset - 



and hairs are for demands close scientific study of each 



particular case, as any other problem does. 



219. Leaves are usually 

 smaller as they approach the 

 flowers (Fig. 159). They 

 often become so much reduced 

 as to be mere scales, losing 

 their office as foliage. In 

 their axils, however, the 

 flower-branches may be borne 

 (Fig. 160). I'uch- reduced 

 leaves, particularly those 

 which are no longer green 

 and working members, are 

 called bracts. In some cases, 

 large colored bracts are borne 

 just beneath the flowers and 



look like petals : the flowering dogwood is an example ; 



also the bougainvillea, which is common in glasshouses 



160. The uppermost flowers are borne 

 in the axils of bracts. Fuchsia. 



