LUMfNOSITY IN PLANTS. 361 



siclered as excellent physiological photometers. This extraordinary 

 light sensitiveness indnced me to test experimentally the heliotropic 

 power of bacterial light. In fact this light can bring about positive 

 heliotropism in various seedlings, such as the lentil, the pea, and the 

 vetch; and in fungi, as Phyeomyces and Xylaria Hyjyoxylon. We 

 have here a striking spectacle, that of one plant influencing another 

 in its movements; the bacteria, by their production of radiant energy 

 in the form of light, compelling the stem of a plant to extend its 

 growth almost direct^ toward the source of illumination. Bacterial 

 light does not, however, show itself capable of causing the production 

 of chlorophyl, probably because the light is not sufficiently intense 

 for this process. 



We come now to the question whether so striking a phenomenon as 

 this development of light in plants gives indication of being of any 

 practical benefit to them. Zoologists seem to agree that light among 

 the animals is of great importance. For when we consider the in- 

 stantaneous and explosive generation of light, the sudden expulsion 

 of a luminous secretion and the wonderful construction of a light-pro- 

 ducing apparatus in animals inhabiting the darkest depths of the 

 sea, we can have no doubt that such constructions are of service to 

 the organisms, and that a definite use is served by this light-devel- 

 opment in the case of many zoological forms. Thus these creatures 

 may, by means of their light, either allure or frighten, or may illumi- 

 nate their surroundings in order to more easily and successfully cap- 

 ture their prey. 



The question in the case of plants is far more difficult to answer. 

 The idea has been advanced that the light capacity of the bacteria 

 may be a means of their distribution. The light of those bacteria 

 occurring in decaying sea animals is said to attract certain animals 

 along the seashore to feed upon these and by scattering the bacteria 

 to aid in their dissemination. I agree with Beijerinck that, as sea 

 currents, waves, and the sand along the shore bring about the dis- 

 semination of these bacteria in the most admirable manner, the before- 

 mentioned opinion is untenable. 



There may be some doubt in the case of luminous mushrooms; in 

 fact, a well-known biologist. Von Kerner, has expressed the opinion 

 that the light of the mushroom points out the way for fungus gnats 

 and fungus beetles, which lay their eggs in the mycelium and si)ore- 

 bearing tissues of these Hymenomycetes ; so that these creatures are 

 in this way of service to the fungus by transporting its spores. At 

 first sight this theory seems to have much in its su])port, but on 

 closer examination we find there is not a littU' against it. Thus, in 

 the case of the mushroom Agnricus vielJens^ it is difficult to under- 

 stand why the gills, which bear the spores and are easily penetrated 

 by insects, are not luminous, while the myceleum, growing under 

 SM 1905 27 



