APPENDAGES TO THE CUTICLE. HAIRS. 



75 



be directed towards the ground, and the roots be made to rise 

 into the air, the little plant will right itself, by twisting itself 

 round, so as to bring its surfaces to their former position. Fur- 

 ther, when plants of a higher description are grown in darkness, 

 the stomata are developed very imperfectly, or not at all. Thus 

 we have an example of the very important effects of the stimulus 

 of light upon the vegetable structure, not only in governing its 

 actions, but in influencing its development. 



96. With the cuticle may be advantageously considered those 

 appendages, which are developed from it, as hairs, prickles, stings, 

 &c. The leaves and stems of many plants are covered with hairs, 

 which is sometimes bristly, sometimes soft and downy, and some- 

 times scattered very thinly. The structure of these hairs is various. 

 Sometimes each forms but one long cell ; whilst in many other 

 instances, every hair consists of a row of cells placed end to end, 

 and sometimes these send off minute side branches. The analogy 

 of these cells with those of the cuticle, is shown by the curious 

 fact, that many plants are hairy, or not, according to the circum- 

 stances in which they grow. Thus, when they are found in dry 

 exposed situations, their stems stunted in growth, and their leaves 



FIG. 33. HAIRS AND GLANDS OP VARIOUS KINES,- a, gland surmounted by a hair; b, 

 small gland at the top of a hair ; c and e, simple hairs ; d, branching hair. 



small, their surface is covered with hairs, as if the cells which 



