u6 INFLUENCE OF THE EXTERNAL CONDITIONS ON GROWTH 



example, either an excess or deficiency of food may suppress the formation 

 of flowers ; in the first case owing to the excessive development of the 

 vegetative parts, and in the second because a starved plant lacks the vigour 

 required for the production of reproductive organs. If not too severe, 

 however, partial starvation usually accelerates the formation of reproductive 

 organs on a previously well-nourished plant. 



When growth is enfeebled by the action of poisons, the plant does 

 not necessarily acquire the same shape as when it is starved. Nor is it 

 surprising that the result produced should depend as much upon the 

 specific character and prevailing condition of the plant as upon the 

 chemical agency applied. Hence no general laws can be laid down for 

 the action of a particular substance. It is, however, certain that changes 

 of shape may be produced by starvation or over-feeding, by a mere change 

 in the proportions or character of the nutriment, by acids, alkalies, and 

 poisons, as well as by enzymes and special stimulatory substances l . All 

 these factors may take part in determining the mode of growth of a plant, 

 the position and character of the various primordia, and hence the shape 

 of the adult plant. It does not, however, follow that particular chemical 

 stimuli are always requisite for the production of sporangia or of flowers, 

 or to determine the subsequent development of a generalized primordium. 



Fungi. Organisms with pronounced powers of adaptation are naturally the 

 ones which respond most markedly to chemical stimuli. This applies especially 

 to those Thallophyta in which the stages of the life-cycle 'are determined by the 

 external conditions. 



The fact that a deficiency of food very often induces the formation of spores 

 is of considerable importance, and in fact the stimulus of partial starvation is 

 required for the production of the spores of "bacteria 2 , the sporangia of 

 Myxomycetes s , and in part also for the spore-formation of Saccharomycetes 4 . 

 Similarly a deficiency of food induces the formation of zygotes in Basidiobohis 

 ranarum'*, and apparently in other Mucorineae also, while the same agency is 

 responsible for the production of zoospores and oospores by Saprolegnia*. The 

 abstriction of conidia begins on the mycelia of Nectria cinnabarina and Ascoidea 

 rubescens when food becomes scanty, and the same cause induces the formation 

 of asci in Ascophanus carneus 1 , and of the sporophore of Coprinus ephemerus 

 (Klebs, 1. c.). 



1 As regards animals see Hertwig, Zelle u. Gewebe, 1898, p. 124. 



2 Buchner, Centralbl. f. Bact., 1896, Bd. xx, p. 806; Schreiber, ibid., p. 431 ; Stephanidis, Bot. 

 Centralbl., 1900, Bd. LXXXII, p. 325 ; Klebs, Jahrb. f. wiss. Bot., 1900, Bd. xxxv, p. 96. 



3 Klebs, 1. c., p. 98. 



* Id., 1. c., p. 94. Various agencies favour spore-formation in non-fermenting yeast. Cf. 

 Hansen, Centralbl. f. Bact., 2. Abth., 1898, Bd. v, p. I ; Jorgensen, Mikroorganismen d. Gahrungs- 

 industrie, 1898, 4. Aufl., p. 195 ; Beyerinck, Centralbl. f. Bact., 2. Abth., 1898, Bd. IV, p. 662. 



6 Raciborski, Flora, 1896, p. 129. 



6 Klebs, 1. c., pp. 91, 102. 



7 Ternetz, Jahrb. f. wiss. Bot., 1900, Bd. xxxv, p. 298. 



