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 



Fir.. 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. 



Fig 





Fig. 180. 



d surface of the cup, >/, 



Fig. 179. — A flower of the red currant cut in half. The rouglu 



secretes nectar. Magnified 5 diam.— After Kerner. 

 In.. 180. I, ,1 petal from the flower ol a buttercup {Ranunculus acris), showing the 



nectary, n. Magnified 3 diam. II, diagram of a longitudinal section ol tin- same 



through the nectary //. 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. 



