PHOTOMORPHIC ACTIONS 91 



but does not pass beyond the embryonic stage described as Chantransta 1 . Very 

 feeble illumination suffices for the germination of moss spores and for the formation 

 of protonemata, but not for the production of the gametophytic buds' 2 . Under 

 similar conditions the germinating spores of liver-worts are often unable to form the 

 embryonic thallus 3 . In such cases, of course, the formation of reproductive organs 

 is suppressed, and, among algae, Vaucheria repens and V. clavata form zoospores 

 in weak light, but sexual organs only under somewhat more intense illumination 4 . 

 The same applies to Oedogonium diplandrum, and the conjugation of Spirogyra 

 is favourably influenced by light 5 . 



Flowering plants. In weak light many flowering plants are unable to 

 pass through all the stages in their development. 1i}\\.\s,Cai}ipajinla rotnndifolia 

 forms only round leaves when feebly illuminated, and, if the light is kept 

 permanently reduced, the shoots bearing elongated leaves ultimately produce 

 round ones G . Again, many plants produce few or no flowers in feeble light, 

 although in others the flowers are able to develop and open in darkness 7 . 



In all herbaceous plants with subterranean bulbous, tuberous, or rhizomic 

 stems (Helleborits, Ranunculus, Narcissus), the first stages in the embryology of 

 the flower are passed through in complete or nearly complete darkness, and 

 hence Senebier's 8 observation, that the flowers of Crocus, Tulipa, &c., are able 

 to carry out their normal development in darkness, is hardly surprising. Sachs 9 

 obtained normally shaped flowers on darkened aerial shoots of Cucurbita, Ipomoea, 

 Phaseolus, and Petunia, the colour also being normal, except in those parts which 

 become green in light (cf. Fig. 20, p. 89). In Cucurbita and Tropaeolum the 

 flower-buds did not merely grow and expand in darkness, but were actually 

 formed ab initio under these conditions. All plants, however, are not able to 

 produce flowers on darkened shoots 10 , and in many cases the stimulus of light 



1 Sirodot, Les Batrachospermes, 1884; Goebel, Hora, 1889, p. 6; Klebs, Biol. Centralbl., 

 1893, p. 646. On other algae see Berthold, 1. c., p. 673. 



2 Goebel, Klebs, 1. c. ; Schostakowitsch, Flora, 1894, p. 358. 



3 Leitgeb, Die Keimung d. Lebermoossporen in ihrer Beziehung zum Licht, 1876, p. 3 (repr. 

 rom Sitzungsb. d. Wien. Akad.) ; Goebel, Klebs, Schostakowitsch, I.e.; Goebel, Organography, 

 1900, I, p. 239. 



4 Klebs, Bcdingungen d. Fortpflanznng, 1896, p. 19. The amount of light required varies 

 somewhat according to the other conditions. 



5 Klebs (I.e., pp. 246, 276) gives other instances. On the prothalli of ferns see Prantl, Bot. 

 Ztg., 1879, p. 701 ; Klebs, Biol. Centralbl., 1893, Bd. xm, p. 652 ; Heim, Flora, 1896. p. 329. 



6 Goebel, Flora, 1896, p. i; Organography, 1900, I, p. 214. Familler (Flora, 1900, p. 95) 

 states that other disturbing influences may induce a production of round leaves in this plant. 



7 Vochting, Jahrb. f. wiss. Bot., 1893, Bd. xxv, p. 155 ; Ber. d. Bot. Ges., 1898, p. 47; Mobius, 

 Biol. Centralbl., 1892, Bd. xil, p. 109; Beitr. z. Lehre v. d. Fortpflanzung, 1897, p. 93 ; Curtel, 

 Ann. d. sci. nat., 1898, 8 e sen, T. vi, p. 269 ; \Viesner, Compt. rend., 1898, May 2. 



8 Senebier, Physik.-chem. Abhandl., 1785, 2. Thl., p. 52. Cf. also de Candolle, Physiol. veget., 

 1832, T. ill, p. 1081. The perianth-tube of Croats becomes longer than usual in complete darkness, 

 its function being to carry the flower up to the light (and air). 



9 Sachs, Bot. Ztg., 1863, Beilage, p. 15; ibid., 1865, p. 117; Arb. d. Wiirzb. Instituts, 1887, 

 Ed. in, p. 387 ; Amelung, Flora, 1894, p. 207. 



10 Vochting, I.e., 1893, p. 177; Askenasy, Bot. Ztg., 1876, p. i ; Walz, Bot. Jahresb., 1875, 

 p. 786. Cf. also Vol. i, 88. 



