238 A TEXT-BOOK OF BOTANY. 



5. Fatty-resins. The resins of this class differ from the others 

 heretofore considered in that they are derivatives of some of the 

 fatty acids. To this group belongs the resinous exudation known 

 as " stick-lac," occurring on a number of trees growing in the 

 East Indies, being caused by the punctures of a hemipterous in- 

 sect, Coccus lacca. 



6. Pigment Resins. In this group are included those exuda- 

 tions in which the resins are combined with a chromogenic deriva- 

 tive. These have been studied but very little, and the best repre- 

 sentative of this class is gamboge, which is used in medicine as 

 well as for coloring in art. 



7. Glucosidal Resins. This group includes, as the name 

 would imply, those resins which are in the nature of glucosides 

 and yield on hydrolysis glucose as well as some other derivative. 

 The resins found in jalap, scammony, and other plants of the 

 Convolvulaceae belong to this group. (Consult A. Tschirch, " Die 

 Harze und die Harzbehalter.") 



ORIGIN OF RESINS. It was at one time considered that the 

 resins were derivatives of tannin. Now that Tschirch has shown 

 that there is a class of resinous substances that give reactions 

 for tannin, it might seem that this theory would receive additional 

 support. However, as he himself explains, the resinotannols con- 

 tain a great deal more carbon than the tannins. Furthermore, 

 Tschirch has shown that a number of the constituents of the 

 resins give color reactions with Liebermann's reagent for phy- 

 tosterbl. On the other hand, a number of these same constituents 

 do not give the characteristic color reaction for phytosterol with 

 Salkowsky-hesse's reagent. With 'regard to the resins of the 

 resinolic acid series, Tschirch concludes that they are probably 

 not derived from volatile oils, but that they are derivatives of a 

 common mother substance. In a later publication Tschirch 

 (" Chemie und Biologic der Pflanzlichen Sekrete ") states that in 

 all probability all the secretory products, formed as a meta- 

 morphosis or decomposition of the resinogenous lamellae, are the 

 direct products of ferments accompanying these layers. 



LATEX OR MILK-JUICE is the product formed in special secre- 

 tory organs in the plant, and exudes readily on even very slight 

 injury of the plant. Under the microscope it is -seen to be in 



