84 THE CUTICLE. 



oblong cells, placed parallel to each other on opposite sides of the 

 aperture, as seen in fig. 34, and have the power of expanding, 

 and thus shutting the orifice, and at others of contracting and 

 curving outwards, and thereby opening it ; thus the respira- 

 tion and evaporation of the plant is controlled by these little 

 cells. Of these we shall speak more particularly when de- 

 scribing the functions of the leaves. With regard to the 

 origin of stomates, considerable discussion has been carried 

 on, but no very satisfactory conclusion has been arrived at. 

 Schleiden and Link are supporters of different opinions. 

 The former supposes that the stomates result from the limit 

 of development of cytoblasts ; that two internal cells are 

 developed, and by the absorption of the parent cells, the 

 space between them becomes the stomata, and that the cells 

 forming the stomatic sphincter differs in no respect from the 

 other cells. The latter believes the stomates are secreting 

 glands, and not mere openings in the cuticle for the transmis- 

 sion of air and gases. 



39. The cuticle gives rise to various little organs which are 

 classed under th6 heads of Mairs, Glandular hairs, Stings, 

 Prickles, Scurf and Lenticels. 



1. Hairs are short acicular bodies found on the surface of 

 many plants, and almost as various in their form as the plants 

 on which they are found. To examine their structure, a good 

 microscope is absolutely necessary. In the spider wort, (Tra- 

 descantia,) the hair is composed of cells placed end to end, 

 and has the appearance of the antennae of insects, and in 

 these cells a circulation is distinctly visible. The sides of 

 these cells are double, although the wall of a cell under com- 

 mon circumstances, appears of simple membrane. That this 

 is not the fact, is proved by permitting the cell to dry on the 

 field of the microscope, and the membranes will separate, and 

 a space is observed between the membranes. It is in this 

 space, that the cinenchyma is located, and in which tissue 



■ the observed circulation goes on. 



2. Glandular hairs, are such as possess the power of se- 

 creting various substances which give the peculiar odor to 

 some plants. They are terminated at the top by an enlarge- 

 ment of the hair sometimes containing cavities in which the 

 secretion is deposited before being set free, at others by a cup- 

 like cavity, answering a similar purpose. 



3. Stings are sharp stiff pointed hairs, which take their 

 rise from the summits of conical reservoirs composed of many 

 separate cells, which are filled with a poisonous fluid secreted 

 by these organs. The sting has an orifice at its summit, 



