132 



PHYSIOLOGICAL BOTANY. 



called a glandular hair (Labiatse). Or it may be a peculiar cell 

 under the epidermis, giving to the organ a punctate appearance 

 (leaf of Lemon). Other glands are compound, and either external 

 (Sundew) or internal reservoirs of secretion (rind of Orange). 



402. Stings are stiff-pointed, 1-celled hairs expanded at base 

 into a gland containing poisonous secretion. An elastic ring of 

 epidermal cells presses upon the gland so as to inject the poisop 

 into the wound made by its broken point (Nettle). 



506 



500 



501 502 



503 



499, Rootlet of Madder, showing cells expanded into fibrilla;. 500, Glandular hair of Fraxinella, sec- 

 tion. 501, Hair of Bryonia, of several cells. 502, Hair of several cells, surmounted by a gland, of An- 

 tirrhinum majiis. 503, Sting of Urtica dioica. 504, Jointed hair of the stamens of Tradescantia. 505, 

 Stellate hair from the petiole of Nuphar advena (magnified 200 diameters Henfrey). 506, Branched 

 Lair, one cell, of Arabis. 



403. Prickles are hardened hairs connected with the epider- 

 mis alone, thus differing from spines, which have a deeper origin. 

 Examples in the Rose. 



Review. What docs the Epidermal System include ? 396. What is the office of the 

 epidermis ? What its cells ? 397. What are the stomata ? When are they open, and 

 when closed ? What of their numbers ? Show them in the figures. 400. What the struc- 

 ture of hairs? 401. What the office of glands? What varieties? 402. Describe the 

 mechanism of the sting (503). 403. Distinguish prickles from spines. Explain the cuts. 



CHAPTER IV. 



THE LIGNEOUS SYSTEM 



Includes the firm structures of roots, stems, and their append- 

 nges, summarily called the woocL 



404. There are four general modes of growth and structure, 



