THE ACTION OF RAYS OF DIFFERENT WAVE-LENGTH 103 



Pilobolus and Coprinus assume the same shape in red light that they do in 

 darkness, and according to Teodoresco (1. c.) plants grow in monochromatic 

 green light just as though in darkness. According to Bert and G. Kraus, 

 however, the green rays accelerate the onset of dark-rigor in the leaves of 

 Mimosa pudica 1 ) and Kraus states they cause the stalk of the fructification 

 of Claviceps microcephala to remain much shorter than in reddish-yellow or 

 blue light or in darkness. It is indeed possible that the isolated green rays 

 may exercise an injurious effect, but nevertheless the above results require 

 further proof, and it needs also to be determined whether the injurious 

 effect is only produced after prolonged exposure, the plants behaving at 

 first as if in darkness. Indeed in all cases the primary effects of the 

 different rays need to be distinguished from the effects following prolonged 

 exposure, and possibly the primary action on growth and on heliotropism 

 would follow similar curves in the absence of any secondary effects. This 

 need not, however, be the case, for heliotropism is a special form of 

 irritability and is not developed in all organs. 



The ultra-violet rays seem also to have a pronounced formative influence, 

 and hence this action is correspondingly decreased when they are removed 

 from ordinary light. In such light, however, the remaining blue rays exert 

 sufficient influence to induce the formation of sporangia and sporophores 

 in Pilobolus and Coprinus 2 , and of sexual organs in Vaucheria 3 . For the 

 same reason the absence of the ultra-violet rays does not produce any 

 immediate effect upon flowering plants, but usually ultimately influences the 

 development as a whole, and in certain cases appears to cause a diminished 

 production of flowers. 



Sachs 4 grew plants of Tropaeolum majus in light passed in one case through 

 water, and in the other through sulphate of quinine, to remove the ultra-violet 

 rays, and found that in the first case numerous, but in the second hardly any 

 flowers were produced. C. de Candolle 5 obtained similar results with this 

 plant, but observed less pronounced differences when Lobelia erinus was cultivated 

 behind quinine sulphate or aesculin solutions, and behind water. Sachs was 

 not, however, justified in assuming that the ultra-violet rays favour the formation 



1 Bert, Mem. d. 1'Acad. d. sc. phys. et nat. d. Bordeaux, 1870, T. vil, p. 28; Compt. rend., 

 1878, T. LXXXVII, p. 695; Kraus, Bot. Ztg., 1876, p. 508. Kraus used alcoholic solutions of 

 cupric chloride, whereas Bert and Teodoresco (1. c., p. 169) employed coloured films. Gerland 

 (Ann. d. Phys. u. Chem., 1878, Bd. CXLVIII, p. 108) found that plants developed behind a solution 

 of chlorophyll as though in weak diffuse daylight. [Either the solutions of chlorophyll were weak, 

 or were not renewed often enough, for behind strong solutions of chlorophyll seedlings of barley, 

 maize, mustard, cress, and castor-oil plant are as much etiolated as in darkness.] 



2 Grantz, I.e., pp. 19, 29; Lendner, I.e., p. 61. Elfving (I.e., p. 40) states that a greater 

 crop of fungus is obtained in the absence of the ultra-violet rays. 



3 Klebs, Bedingungen d. Fortpflanzung, 1896, p. no. Cf. also M. E. Pennington, Contr. from 

 the Bot. Lab. of the Univers. of Pennsylvania, 1897, Vol. I, p. 250. 



* Sachs, Arb. d. Bot. Inst. in Wiirzburg, 1887, Bd. Ill, p. 372. 



5 C. de Candolle, Archives d. sci. phys. et nat. d. Geneve, 1892, T. xxvm, p. 265. 



