24 CUTICLE AND EPIDERMIS. 



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

 and a space be observed between the membranes. It is in thu 

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

 observed circulation goes on. 



40. Glandular Hairs are such as possess the power of secre- 

 ting various substances which give the peculiar odor to somt 

 plants. They are terminated at the top by an enlargement oi 

 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. 



41. 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, con- 

 nected with the cells containing the acrid secretion ; and, by the 

 force required to pierce the skin, it presses upon the cavities 

 which propels the fluid up the tube, and injects it into the wound 

 made by the point. It is this poison which causes the severe 

 pain occasioned by the sting of the nettle. 



42. Prickles are hard, sharp-pointed, stiff productions of the 

 cuticle, often hooked at the extremities. When the prickles 

 have acquired their full growth, they are quite firmly attached 

 to the stem ; but as the stem advances in size, the prickles, re- 

 maining of the same dimensions, become loosened at their base 

 and fall off. Hence, old stems are seldom covered with prick- 

 les, while the younger ones are prickly. 



43. Scurf or Lepides, appearing to the naked eye like a 

 mealy substance on some leaves, are scales attached to the stem 

 by their center, and seem to be formed by the cohesion of many 

 hairs having the same point in the cuticle for their origin. 



44. Lenticels are brown spots appearing on the stems of 

 many trees and shrubs, at first nearly round, but as the stem 

 increases in size, they assume a linear form, and produce trans- 

 verse spots on the surface of the stem, as may be seen in the 

 Cherry, Willow, Birch, and other trees and shrubs. By a closer 

 examination, we find the lenticels to consist of a corky sub- 

 stance apparently projecting through apertures in the cuticle, 

 and being divided into two lips by a medial slit. By cutting 

 through one of these lenticels transversely, and examining it with 

 a microscope, the student will find that they are placed on the 

 external layer of the bark, between it and the epidermis, and 

 that it has no connection with the bark, much less with the wood. 



40. Describe glandular hairs. — 41. What are stings? — 42. What are 

 prickles ? — 43. What is scurf? — 44. What are lenticels ? 



