NUTRITION. 



1 77 



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 



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

 of the disorganization of the oil-producing cells ; b, 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, n, 



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, b, secretes the drop 



of nectar, /. Magnified 8 diam. — After Behrens. 



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

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

 are dropped. 



