CHAPTER XVI. 



ACCESSORY CHARACTERS OF TWIGS. 



Bloom Hairs Pubescence and other forms of hairiness Bristles 

 and Prickles Spines and Thorns Morphology of thorns 

 Climbing organs Parasites and Epiphytes Twiners and 

 tendril-climbers Morphology of tendrils. 



IT now remains to specify a series of the accessory 

 characters of twigs, which sometimes profoundly affect 

 their appearance, and which naturally fall into two prin- 

 cipal categories. 



In the first of these we have a number of epidermal 

 peculiarities, where the structures are superficial and can 

 generally be easily removed by rubbing or by tearing off 

 the outer skin only. The second category comprises 

 structures belonging to, or including in their composition, 

 tissues lying beneath the epidermis, and which can only 

 be removed by cutting or seriously injuring the con- 

 tinuity of the anatomy of the twig. 



Among the former, we include the waxy bloom, 

 already referred to in Salix daphnoides. This consists 

 of a thin layer of wax, excreted by the cuticle or outer- 

 most layer of the epidermis, in the form of minute scales 

 or granules, which cause peculiar reflections of the light 

 and enable water to roll off easily, much as it does off the 



