NUTRITION. 



177 



chouc and gutta-percha occur in the milky juice of certain 

 plants. 



253. Nitrogenous by-products. Among the nitrogenous 

 waste materials the most important are the alkaloids, such as 



FIG. 178. Section through oil-receptacles in rind of orange, a, structure at the beginning 

 of the disorganization of the oil-producing cells; /', final condition, with two drops of 

 oil occupying the cavity. Moderately magnified. After Tschirch. 



I II 



FIG. 179. FIG. 180. 



FIG. 179. A flower of the red currant cut in half. The roughened surface of the cup, , 



secretes nectar. Magnified 5 diam. After Kerner. 

 FIG. 180. I, a petal from the flower of a buttercup (Ranunculus acris), showing the 



nectary, n. Magnified 3 diam. II, diagram of a longitudinal section of the same 



through the nectary n. The tissue lining the pouch of the petal, /', secretes the drop 



of -nectar, t. Magnified 8 diam. After Behrens. 



quinine, morphine, strychnine, nicotine, etc., which occur in 

 the seeds, bark, or leaves, and arc gotten rid of when these 

 are dropped. 



