172 



TEXTBOOK OF BOTANY 



reduction processes. Others appear to be of no particular value or detri- 

 ment to the species in which they are formed. Before chemists learned 

 how to make dyes in the laboratory man was dependent solely upon these 

 natural dyes. Among the more important are annatto, camwood, fustic, 

 henna, indigo, litmus, logwood ( haematoxylin ) , madder, red sandal- 

 wood, saffron, and tuiTneric. 



Resins, gums, and mucilages. Resins are insoluble in water and render 

 cell walls impervious to it. They occur usually in definite glandular struc- 

 tures, or in tubes extending throughout the plant. Amber is a fossil resin. 

 Resins are soluble in alcohol and certain oils. Commercially they are used 

 in the preparation of a variety of varnishes, soaps, dyes and medicines. 

 Resin is one of the important products of the pine forests of the south- 

 eastern United States (Fig. 63). 



Fig. 63. Method of tapping southern long leaf pine to collect resin. 



Gums and mucilages are much alike. They are insoluble in alcohol 

 and become jelly-like in water. Upon drying, gums first become sticky 

 and then hard. Mucilages swell greatly in water. They may be im- 

 portant in holding water in the plant tissues in which they occur. Com- 

 mercially they are important bases of various mucilages and chewing 

 gum. 



Latex. Many plants, such as the milkweeds, euphorbias, figs, and 

 rubber plants, have a milky colloidal "juice" called latex. This is a mix- 



