THE INFLUENCE ON FORM AND STRUCTURE 123 



Similar powers of accommodatory response are possessed by fungi. Thus 

 Klebs * has found that Sporodinia grandis, Penicillium, and Aspergillus form no 

 sporangia under water, or in air saturated with moisture. This is because tran- 

 spiration supplies the stimulus for their formation, although not for the production 

 of zygotes, which is favoured by damp air. Hence by varying the moistness of 

 the air the production of sporangia or of zygotes can be induced at will. 

 Eurotium, on the contrary, usually forms conidia when the supply of water 

 diminishes. In certain fungi the spores and sporangia normally appear under 

 water, so that it is not surprising that Mortierella van Tieghemi is able to produce 

 its sporangia in fully saturated air in which no transpiration is possible 2 . Other 

 factors may also enter into play, and the influence of the percentage of oxygen 

 on the formation of sporangia, though slight in the case of Sporodinia^ is pro- 

 nounced in that of Mortierella. 



The shapes of algae vary widely according to whether they grow submerged 

 or on damp substrata. Moreover Vaucheria forms zoospores when transferred 

 from damp soil to water, and in running water the formation of sexual organs 

 is suppressed 3 . Whether the water acts mechanically or as an inhibitory stimulus 

 is uncertain 4 . 



The formation of primordia is not always affected to the same degree as the 

 subsequent development. Thus certain aquatic plants form flower-buds under 

 water, but these do not open, whereas in other cases immersal in water injuriously 

 affects the development of primordia formed in air 5 . Further, a deficiency of 

 water affects the formation of root-primordia less than it does their subsequent 

 growth, while immersal in water accelerates the latter 6 . 



The action of saline solutions is not the same as when the turgor is diminished 

 by transpiration. Hence even when the former only act osmotically, they do not 

 always produce the same changes of shape as result from a fall of turgor due to 

 increased transpiration 7 . 



1898, Bd. LXXIV, p. 184; Jahn, Fiinfstiick's Beitr." z. wiss. Bot., 1897, I, p. 281; Lazniewski, 

 Flora, 1896, p. 260; Schimper, Pflanzengeographie', 1898, p. 20. On the influence of moisture on 

 the development of hairs, thorns, &c., cf. Goebel, Organography, 1900, p. 262. 



1 Klebs, Jahrb. f. wiss. Bot., 1898, Bd. xxxn, p. 61 ; 1900, Bd. xxxv, p. 115; Ternetz, 

 Jahrb. f. wiss. Bot., 1900, Bd. xxxv, p. 298; Schmid, Bot. Centralbl., 1898, Bd. Lxxvi,p. 302. 

 According to Celakovsky (Bot. Centralbl., 1900, Bd. LXXXiil, p. 292), sporangia and conidia 

 develop in oil, i. e. in the absence of transpiration, so that the transition to the new medium must act 

 in some other way. 



2 Bachmann, Jahrb. f. wiss. Bot., 1899, Bd. xxxiv, p. 323. Cf. Klebs, 1900, 1. c., p. 122. 



3 Klebs, Bedingungen d. Fortpflanzung, 1896, p. 223. 



4 Cf. Klebs, ibid., p. 441 (Hydrurus}; Goebel, Pflanzenbiol. Schilderungen, 1893, 2. Theil, p. 441. 



5 Grantz, Einfluss d. Lichts auf einige Pilze, 1898, p. 61. 



6 Vochting, Organbildung i. Pflanzenreich, 1878, pp. 125, 142; Pfeffer, Arb. a. d. Bot. Inst. in 

 Wurzburg, 1871, Bd. i, p. 97. 



7 Schimper, Pflanzengeographie, 1898, p. 98 ; Diels, Jahrb. f. wiss. Bot., 1898, Bd. xxxn, p. 308 ; 

 Dassonville, Rev. gen. d. Bot., 1898, T. x, p. 15 ; Otto, Ber. d. Bot. Ges., 1899, p. 139 ; Eberhardt, 

 Compt. rend., 1900, T. cxxxi, pp. 193, 513; Beauverie, Compt. rend., 1901, T. cxxxn, p. 226. 

 On algae cf. Famintzin, Melang. biol. d. Bull. d. 1'Acad. de St.-Petersbourg, 1871, T. vni, p. 226. 



