CELL-CONTENTS AND FORMS OF CELLS. 171 



tissues of the plant. With very few exceptions, however, the 

 color reactions are not satisfactory. 



MICRO-CHEMISTRY OF GLUCOSIDES. Although the glucosides 

 upon extraction from the plant tissues form well-defined crystals 

 (Fig. 99), they have not been identified as such in the plant. 

 A few have been identified by giving distinct color reactions with 

 certain reagents. The glucoside strophanthin can be detected in 

 the seeds of Strophanthus hispidus. This glucoside is colored a 

 brilliant green with sulphuric acid and is confined to the cells of 

 the endosperm. The test is carried out as follows : Sections 

 are mounted first in water and then transferred to a drop of 

 sulphuric acid contained on the same slide, when the cells con- 

 taining strophanthin are colored a bright green. Saponin is an- 

 other glucoside which, it is stated, may be readily detected in 

 plant cells, giving a reddish color reaction with sulphuric acid. 

 Lafon's reagent also may be applied for the detection of saponin ; 

 this consists in the use of two solutions: (a) equal volumes of 

 alcohol and sulphuric acid; (b) a very dilute solution of ferric 

 chloride. The sections are placed in solutions (a) and then a 

 drop of solution (b) is added. Cells containing saponin are col- 

 ored red, changing to violet, becoming brownish-blue, or brown 

 upon the addition of ferric chloride. Coniferin, the glucoside 

 found in the cells of pine and other Coniferous trees, is colored 

 red with sulphuric acid ; it also gives a characteristic reaction on 

 treatment of the section first with phenol, followed by sulphuric 

 acid or hydrochloric acid, it becoming a deep blue almost instantly. 



THE SAPONINS are a group of glucosides which possess the 

 common property of forming a froth on shaking their aqueous 

 solutions, and are present in the " soap-plants," which have 

 been widely used as detergents. The saponins also dissolve the 

 red blood-corpuscles, and for this reason are considered to be 

 toxic substances. They have been found in the cell-sap of a large 

 number of plants, occurring in parenchyma cells and medullary 

 rays of roots and stems, the secretion cells and secretion reser- 

 voirs of leaves, and all parts of fruits and seeds. A large number 

 of principles have been isolated from different plants, some of 

 these being given distinct names, but the majority of them are 

 homologous substances having the general formula C n H 2n _ 8 O 10 . 



