PIPSISSEWA 



505 



If the material thus treated is placed upon a watch crystal, which is 

 covered with another watch crystal, or a slide and gently heated upon 

 an iron plate, or a strip of asbestos, a microsublimate of hydrochinon 

 may be collected. The latter consists of long monoclinic rods and 



FIG. 214. Chimaphila umbellata: A, transverse section of an aerial internode: 

 Ep, thick-walled, somewhat papillose epidermal cells; H, hypodermis 

 composed of thick-walled collenchymatous cells; P, cortex of parenchyma 

 traversed by very wide air-spaces (A), due to the separation of the cells 

 in several of the middle layers. The parenchyma contains chloroplastids 

 which are not here shown; and in the air-spaces in alcoholic material there 

 are usually numerous sphsero-crystals. B, transverse section of a portion 

 of the pith of an internode, showing the moderately thickened parenchyma, 

 intermixed with very thin-walled, irregular cells, which contain rosette 

 aggregates of calcium oxalate. C, transverse section of the ventral epi- 

 dermis showing the heavily thickened outer walls. D, surface view qf the 

 dorsal epidermis showing the thick, porous walls of the epidermal cells, and 

 the characteristic stomata which lack subsidiary cells. The guard cells of 

 the stomata are slightly raised above the surrounding epidermis, and the 

 wide air-chambers are very shallow. After Holm, Merck's Report, 1909 

 p. 143. 



feather-like aggregates, which polarize light with a brilliant play of 

 colors. Among confirmatory tests the following may be employed. 



