176 



PLANT LIFE. 



crystallization (fig. 176). The resins, usually dissolved in 

 an oil, are generally excreted into special intercellular spaces 



Fig. 176. Crystals found in plants. I, calcium carbonate; II-V, calcium oxalate; 

 II, octahedron with blunt ends ; III, compound crystals from the nectary of a mallow; 

 IV, a, b, needle crystals (raphides) from leaf of fuchsia ; V, cell from the fruit-flesh 

 of a rose showing a crystal, k, embedded in an outgrowth of the cell-wall, c. All highly 

 magnified. — After Behrens. 



Volatile oils are secreted by glandular hairs 

 (c, fig. 113); or are formed 

 in the epidermis itself, as in 

 flowers ; or are produced in 

 chambers near the surface, 

 the cells which produce the 

 oil being disorganized to 

 form the cavity in which 



Fig. 177. — Transverse section of an inter- 

 cellular receptacle for gum-resin from the the drops lie (rig. 17")- 

 fruit of fennel. The secretion has been 



dissolved out by alcohol. The shaded cells Other materials, SUCh as 

 lining the tube are the secretory tissue. 

 Moderately magnified.— After Tschirch. salts of lime, are Sometimes 



excreted upon the surface of the plant. From glands in 

 the flower, nectar, which is a solution of sugar, is excreted 

 (figs. 179, 180). The loss of this food is compensated for 

 by its attractiveness for insects, which incidentally serve for 

 the transfer of pollen from one flower to another. Caout- 



