498 CONSTRUCTirE AND DESTRUCTIVE METABOLISM 



barillas'. If the exposure has not been too prolonged, the power of pigment 

 formation may gradually return in the successive generations produced under 

 normal conditions, but by more drastic treatment this power may apparently be 

 permanently destroyed 2 . 



SECTION 89. Alkaloids, Ptomaines, and other Poisons. 



Numerous plants produce one or more poisonous substances, including 

 alkaloids, ptomaines, toxalbumins 3 , certain glucosides, and other chemical 

 substances, such as hydrocyanic acid, &c. (cf. Sect. 70). 



Some of these substances are virulent poisons, and have for the most 

 part a biological importance, forming a protection against herbivorous 

 animals and against the penetration of parasites 4 . They may also 

 enable certain plants, especially bacteria, either to compete successfully 

 with other organisms, or by killing the latter to provide for their own 

 growth (Sect. 92). For the latter purpose it is obviously essential that the 

 poisonous products should be excreted, but in many of the higher plants 

 and fungi they are permanently retained and deposited in a manner best 

 suited for the fulfilment of their special biological importance ; as, for 

 example, when poisons accumulate in the fluid latex which at once carries 

 to an injured region both material for repair and a means of defence against 

 further attacks 5 . Within living cells poisons are generally deposited in 

 the cell-sap, and in this way as well as by the attainment of a certain 

 immunity, large quantities may be accumulated without injury to the 

 poison-producing plant. Certain fungi are capable of feeble growth on 

 dilute solutions of morphia, &c., but as a general rule such poisonous 

 substances, when produced by the plant itself, do not appear to be re- 

 assimilated, as is instanced by the behaviour of the solanin of the potato 

 during germination 6 . Although in this case, as well as during the germina- 

 tion of the seeds of Datura Stramonium and StrycJinos mix vomica, a 



1 Schottelius, Centralbl. f. Bact., 1887, Bd. n, p. 439. Cf. Fliigge, I.e., p. 487; Charrin et 

 Phisalix, Compt. rend., 1892, T. cxiv, p. 1565; Laurent, Ann. d. 1'Inst. Pasteur, 1894, T. xiv, 

 p. 479. 



a Galeotti, Centralbl. f. Bact., 1893, Bd. xiv, p. 697 ; Dieudonne, Biol. Centralbl., 1895, Bd. xv, 

 p. 109. 



'' Cf. Neumcister, Physiol. Chemie, 1893, p. 226; Hoppe-Seyler, Handb. d. chem. Analyse, 

 4. Aufl., 1893, p. 94. 



* Cf. lit. in Sect. 87. Peirce has shown that the penetration of Cuscnta into a host-plant is 

 hindered by the presence of poison in the latter, and the same is the case with fungi. 



6 Cf.Zimmermann, Mikrotcchnik, 1892, p. 116; Moller, Localisation d. alcaloides d. Solanacees, 

 Bruxelles, 1895. 



6 De Vrics, Landw. Jahrb., 1878, Bd. vil, p. 243; Wotezal, Bot. Jahresb., 1890, Bd. XLI, 

 p. 100 ; G. Meyer, Beibl. z. Bot. Centralbl., 1896, Bd. vi, p. 61. 



