CHANGES OF FORM PRODUCED BY CHEMICAL AGENCIES 117 



These responses are best shown when the previous nutritive conditions were 

 such as to permit of active vegetation. If the plants are too much starved, or 

 their growth almost suppressed by alkalies, acids, or poisons, the production 

 of reproductive bodies almost or entirely ceases. Feeble vegetative growth is 

 also possible under conditions which do not permit of the inception of new 

 developments, and we have already seen that, as regards temperature and light, 

 the maxima and minima for vegetative growth are further apart than for repro- 

 ductive activity. The same applies in the case of oxygen, a smaller quantity of 

 which suffices for the production of the simpler reproductive organs, than for 

 those of morphologically higher value. Thus according to Klebs l the sporangia 

 of Sporodinia grandis are formed in air reduced to a pressure of 15 mm. of 

 mercury, whereas the production of conjugating hyphae begins when the pressure 

 is raised to 20 mm., and actual conjugation only takes place above 60 mm. 

 pressure (= air with 1-7 per cent, of oxygen). Van Tieghem and others errone- 

 ously supposed that the formation of zygotes was induced by a deficiency of 

 oxygen 2 , but this latter does actually cause or favour the passage of the plasmodia 

 of Myxomycetes into certain resistant forms. In the case of anaerobic bacteria 

 it is apparently, on the contrary, the presence of oxygen which induces the formation 

 of spores, or other resting conditions. 



In some cases inequalities in the distribution of food produce growth-responses, 

 and the quality of the food-materials is also of importance. Thus, according to 

 Klebs 3 , Saprolegnia grows very well upon meat-extract, peptone, or gelatine, but 

 produces no reproductive organs, whereas glutamin, asparagin, and an abundance 

 of phosphates favour the development of oogonia. 



These agencies, as well as acids, alkalies, and poisons, also influence vegetative 

 activity 4 . Thus fermenting Mucor-yeast is not only produced when the organism 

 grows immersed in nutrient sugary solutions in which the supply of oxygen is 

 scanty, but also to a greater or less extent under the action of citric acid and 

 other external agencies 5 . In addition to Mucor certain other fungi form yeast- 

 like growths under the action of the same and other agencies 6 . On the other 

 hand the shapes of various species of Saccharomyces 1 * are influenced by the 

 cultural and nutrient conditions, and the same also applies to many bacteria 8 . 



1 Klebs, Jahrb. f. wiss. Bot., 1898, Bd. xxxil, pp. 66, 132 ; ibid., 1900, p. 92. 



2 Cf. Klebs, 1. c., 1900, p. 133. 



3 Id., 1. c., 1890, p. in. 



* See also Matruchot, Rech. s. 1. de*vel. d. Muce"din., 1892 ; Bachmann, Bot. Ztg., 1895, p. 107; 

 Jahrb. f. wiss. Bot., 1899, Bd. xxxiv, p. 322 ; Planchon, Ann. d. sci. nat., 1900, 8 e ser., T. xi, 

 p. i ; Werner, Die Bedingungen d. Conidienbildung bei einigen Pilzen, Dissert., 1898 ; Ensch, Notes 

 s. 1. Myxomycetes, 1899. 



5 See Klebs, Bedingungen d. Fortpflanzung, 1896, p. 509, and the literature there given. 



6 Id., I.e.; also Zopf, Pilze, 1890, p. 17; Schostakowitsch, Flora, 1895, Erg.-bd., p. 362; 

 Raciborski, Flora, 1896, p. 126. 



7 Hansen, Compt. rend. d. Labor, d. Carlsberg, 1900, T. v, p. i ; Jorgensen, Mikroorganismen 

 d. Gahrungsindustrie, 1898, 4. Aufl., p. 195, and the literature there given. 



8 Fltigge, Mikroorganismen, 1896, 3. Aufl., Bd. I, pp. 52, 430, 478, &c. ; Migula, System d. 

 Bact., 1897, Bd. i, pp. 173, 212. On acetic bacteria, cf. Hansen, Centralbl. f. Bact., 2. Abth., 1895, 

 Bd. i, p. 36 ; Compt. rend. d. Labor, d. Carlsberg, 1900, T. v, p. 39 ; Henneberg, Centralbl. f. Bact., 

 1898, 2. Abth., Bd. iv, p. 1 6. 



