spines and Tendrils 



6i 



If all the normal buds of the plant were developed, the 

 branching would follow regularly the arrangement of the leaves. 



This uniformity is often interfered with : ist, by the non- 

 development of buds ; 2nd, by the formation of adventitious 

 buds. 



Sometimes many of the buds remain entirely undeveloped. 

 At other times, instead of being developed into leaf-bearing 

 branches, they form subsidiary organs. 



1. Spines are often modified branches. They are met with 

 in the Sloe or Blackthorrl. At times they are small and desti- 

 tute of leaves ; often they bear leaves, and under cultivation 

 they become developed into leaf-bearing branches. Thus, 

 whilst the Sloe is spiny, the 

 cultivated Plum bears only 

 leafy branches. 



There is a great difference 

 between spines (as in the Sloe 

 and Locust-tree) and prickles 

 (as in the Rose and Bramble). 

 In the former case the spines 

 are modified branches, and as 

 such are connected with the 

 internal parts of the stem ; in 

 the latter case the prickles are 

 simply hairs of the epidermis 

 which have become hardened 

 by the deposition of secondary 

 deposit. 



2. Tendrils. — Sometimes 

 the buds become developed 

 as tendrils or cirrhi, as in the 

 Grape Vine, enabling the plant 

 to hold on to the object of 

 support. 



Both spines and tendrils may be modifications of parts of 

 leaves. The spines of the Barberry, and of some species of 

 Acacia (fig. 129), and the tendrils of the Sweet Pea (fig. 93), 

 are examples. 



Fig. ^2.— Stem tendrils of the Grape-vine : 

 7/, in the normal state ; v, bearing a 

 bunch of grapes. 



