SECT. I 



MORPHOLOGY 



97 



seed coats of various species of Gossypium attain an unusual length, 

 and supply the cotton of commerce (Fig. 108). These cotton hairs are 

 sometimes 6 cm. long, and in their fully-developed state contain only 

 air ; their cell walls are thicker than those of ordinary hairs, and 

 covered with a delicate cuticle. They are usually somewhat flattened 

 and at the same time twisted ; and are wider in the middle than at 



Fig. 111. — Glandular hair from the 

 petiole of Primida sinensis. 

 (After De Bary, X 142.) 



Fig. 110. — A, Spindle -shaped hair from the under 

 surface of a leaf of the Wallflower, Chdranthus 

 cheiri; B, cross-section of leaf showing inser- 

 tion of hair; C, stellate hair and adjoining 

 epidermis from the under side of a leaf of 

 the Stock, Matthiola annua. (A, G, x 90 ; B, 

 X 240.) 



Fig. 112.— Glandular scale from the 

 female inflorescence of the Hop, 

 Mumulus Lupulus, in vertical 

 section. A, before, B, after the 

 cuticle has become distended by 

 the excretion. In B the ex- 

 cretion has been removed by 

 alcohol. (After DeBary, x 142.) 



either end (Fig. 108, _B 2 ). Bkistles are short, pointed hairs, in the 

 thickened cell walls of which calcium or silica has been deposited 

 (Fig. 109, below, to the right). 



The stinging hairs (Fig. 109), such as those of Nettles ( Urtica) and 

 of the Loasaceae, are special forms of bristles, and arise as prolongations 

 of single epidermal cells. These however, swell in the course of their 

 development, and becoming surrounded by adjoining epidermal cells pre- 



