INFLUENCE OF CHEMICAL AGENCIES ON GROWTH 113 



These facts are important because they show that a general or local 

 retardation, or a reawakening of growth, may be produced in a self-regulatory 

 manner by the products of the plant's own activity, and the former may 

 occur even when the supply of food and the other external conditions are 

 at an optimum. Similar results may apparently be produced not only by 

 the quantity, but also by the quality of the food supplied, so that a seed 

 or spore amply supplied with stored food-materials may only be able to 

 germinate when a particular nutrient solution, or nutrient or non-nutrient 

 substance, exerts an exciting chemical stimulus upon it. In fact the 

 importance of a food-material is not to be measured solely by the 

 supply of energy it yields, and by its use for constructive metabolism, 

 as is instanced by the important effects exercised by ferments and by 

 small traces of iron. 



After treatment with ether the temporary retardation of the growth of seedlings 

 is followed by a temporary acceleration above the normal rate \ Excessive doses 

 act injuriously, and weak ones produce little or no effect, so that the results of 

 different authors are frequently contradictory 2 . 



The spores of certain fungi are unable to germinate unless subjected to certain 

 chemical stimuli. Thus Duggar 3 found that the spores of Botrytis vulgaris will 

 germinate on pure water, but not those of Aspergillus flavus, A. niger, Penidllium 

 glaucum, and Phycomyces nitens. After resting on paraffin, however, all the spores 

 of Aspergillus flavus, and most of those of A. niger, develop a long germ-tube, and 

 a certain percentage of the other spores can be caused to germinate by special 

 stimulation. On a nutrient solution the direct influence of the food absorbed 

 and its indirect stimulating effect may act conjointly upon germination, as well as 

 upon the subsequent development. In darkness, for example, sugar and, to a less 

 extent, peptone excite the germination of moss-spores, which in light takes place 

 on pure water 4 . 



The spores of Mendius lacrymans* germinate only on alkaline media, and 

 those of Onygena equina only after they have been subjected to the action of 

 the gastric juice 6 . Further researches will probably reveal other special pecu- 



1 Townsend, Annals of Botany, 1897, Vol. XI, p. 522. 



2 Detmer, Landw. Jahrb., 1882, Bd. XI, p. 227 ; Elfving, Einwirkung von Aether n. Chloroform 

 auf Pflanzen, 1886, p. 12 (Ofvertryck af Finska Vet. Soc. Forh., Bd. xxvm) ; Tassi, Bot. Jahresb., 

 1887, p. 27; Heckel, ibid., 1889, p. 12 ; Sandsten, Minnesota Bot. Studies, 1898, 2nd ser.. Vol. I, 

 p. 53. On the influence of CO 2 , see Lopriore, Jahrb. f. wiss. Bot., 1895. Bd. xxviil, p. 623; 

 Jensen, Centralbl. f. Bact, 1900, Bd. vi. p. 762 (yeast) ; On the action of tartrate of iron on Zygnema, 

 see Klebs, Unt. a. d. Bot. Institut in Tiibingen, 1886, Bd. II, p. 545. 



3 Benecke (Jahrb. f. wiss. Bot, 1895, Bd. xxvm, p. 501) observed that the spores of certain 

 fungi do not germinate in the absence of potassium. 



4 Goebel, Flora, 1896, p. 75; Heald, Gametophytic Regeneration, Leipz. Dissertat., 1897, p. 54. 



5 R. Hartig, Der echte Hausschvvamm, 1885, p. 25. 



6 Ward, Phil. Trans., 1899, Vol. CXCI, p. 278. Cf. de Bary, 1. c., p. 376. 



PFEFFER. II I 



