184 



PLANT PHYSIOLOGY 



Whether the alkaloids are waste products from nitrogenous 

 materials or are direct synthetic products has not been deter- 

 mined. According to Annett (1920), the morphine alkaloids are 

 waste products of the poppy and the latex system serves to get 

 rid of them. Baly thinks the alkaloids are waste materials which 

 tie up the waste nitrogen in an insoluble and harmless form. 

 Certainly they are not necessary for the plant which bears them, 

 as is shown by Lotsy (1900) in the case of the cinchona tree, which 

 thrives well in hothouses but makes no quinine. Certain of the 

 Thallophytes can use alkaloids as food if in a dilute state. Accord- 

 ing to Comere (1910) fungi have been found to use small amounts 

 of morphine, and certain algae have been able to use atropine, 

 cocaine, and morphine but not quinine or strychnine. Calutriau 

 (1900) reports that higher plants cannot use alkaloids as the sole 

 source of nitrogen. Although plants produce more alkaloids in the 

 sunlight than in the shade (Goris and Deluard report twice as 

 much in Atropa belladonna), this offers no clue to their function. 

 Whether useful in protein synthesis or merely waste products 

 therefrom, one would expect more to be formed in the sunlight. 



In small amounts, alkaloids stimulate the germination of seed 

 and the development of seedlings, according to Longo and Paderi 

 (1929), who concluded that alkaloids might serve as regulators 

 and stimulators of metabolism. On the other hand, nicotine has 

 been found toxic to the germination of tobacco seed; and some 

 workers see in the toxic nature of alkaloids their chief survival 

 value. They are thus considered to protect the plants against 

 destructive enemies such as browsing animals and insect pests. 



The Purine Bases. — These are all derivatives of the same 

 substance, purine (C 5 H 4 N 4 ). Adenine (wheat, beets, tea, and 

 clover), caffeine (tea and coffee), and theobromine (cocoa) are 

 among the better known purine bases found in plants. If the 

 structural formulae of caffeine and purine are compared, the re- 

 lationship will be evident. 



N=CH 



HC C— N 



CH 3 N— C=0 



H 



CH< 



0=C C— N 



N— C— N 



/ 



CH 



i 



CH 3 N— C— N 



>CH 



purine 



jaffeine 



