94 SCIENCE PRIMERS. [xxin. 



probably intended to prevent its injurious effects on 

 the subjacent tissues. Others are hairs and scales. 



Hairs are either prolongations of epidermal cells, 

 or single long cells of the epidermis (cotton), or 

 strings of such cells (spider-wort). They are protec- 

 tions against wet, cold, and the effects of drought on 

 the subjacent tissue. They are often branched (mal- 

 low) or radiate from a point, like a star; when the 

 rays of such a star are combined the result is a scale 

 or scurf (elaeagnus.) 



(b) Defensive. The sting of the nettle is a single 

 awl shaped rigid cell, with a swollen base, in which an 

 irritating fluid is secreted. On piercing the skin the 

 point breaks off, and the fluid is deposited in the wound. 



(c) Attractive. Hairs that secrete a fluid which 

 is sugary or odorous are very common (sweet briar), 

 and are no doubt intended to attract birds and insects 

 for the purpose of fertilizing the flowers or carrying off 

 and thus dispersing the seeds. 



(d) Nutritive. The glandular hairs of the sun- 

 dew, which both retain the insects that visit the leaves 

 (thus acting also as detentive organs) and absorb 

 nutriment from them. The sticky stems of the catch- 

 fly, and many other plants, probably serve the same 

 purpose. 



(<?) Scansorial (aids to climb). Such are especi- 

 ally prickles, which are hooked cellular growths from 

 the epidermis. By their aid the bramble and many 

 roses climb bushes, and so get to the light. By their 

 aid the rope-like rattan-canes of the Indies ascend the 

 loftiest forest-trees, and expand their crown of foliage 

 and flowers in the sun. They must not be confounded 

 with spines (Par 65). 



