110 PHARMACEUTICAL BOTANY 



usually resembles the other parenchyma layers of cortex as to struc- 

 tural characteristics, save that it frequently contains more starch. 

 In fern stems, roots of Monocotyledons and of Dicotyledons of 

 primary growth, however, its cells are clearly distinguished from the 

 other cells of the primary cortex by their elongated form and sub- 

 erized (occasionally lignified) radial walls. In the roots of Mexican 

 Sarsaparilla the inner as well as the radial walls are suberized; in 

 those of the Hcnduras variety, inner, radial and outer walls all show 

 suberization. Endodermal tissue is devoid of intercellular-air-spaces. 

 Its cells contain protoplasm and nucleus. Its functions seem to be 

 to give protection to the stele (tissues within it) and to reduce per- 

 meability between primary cortex and stele. 



CORK 



Cork or suberous tissue is composed of cells of tabular shape, 

 whose walls possess suberized layers. Its cells are mostly filled 

 with air containing a yellow or brownish substance. It is derived 

 from the phellogen or cork cambium which cuts off cork cells out- 

 wardly. Cork tissue is_ devoid of intercellular-air-spaces. It 

 forms a protective covering to the roots of secondary growth, stems 

 (after the first season) of Dicotyledons and Gymnosperms, and 

 wounds of stems and branches. Living cork cells contain protoplasm 

 and cell sap while dead cork cells are filled with air. 



The walls of cork cells resist the action of concentrated sulphuric 

 acid. They are colored green, when in contact with alcoholic 

 extract of chlorophyll for several days in the dark. 



LATICIFEROUS TISSUE 



This form of tissue comprises either latex cells, laticiferous vessels, 

 or secretory cells differing from each other in origin and method of 

 development. Latex cells are elongated tubes which take their' 

 origin from meristematic cells of the embryo. Elongating with the 

 growth of the plant, they branch in various directions and traverse 

 at maturity all of its organs. Such cells are abundant in the 

 following families: Apcoynacece, Asclepiadacea, Urticacea and 

 Euphorbiacea. 



