Apeil 22, 1910] 



SCIENCE 



619 



tivity of land forms in spring, but Herdman 

 says' that " the temperature of the sea-water, 

 however, appears to have little or no efiect in 

 determining the great vernal maximum of 

 phyto-plankton." From this it is presumed 

 that the richness decreases in the summer in 

 spite of the warmer water, because the light 

 becomes more or less destructive. It must be 

 remembered that at 70° of north latitude the 

 midday sun is just as strong on June 22 as it 

 is at the tropic of cancer December 22. 



There seems to be great confusion in litera- 

 ture on the effects of light, due to failure to 

 distinguish between these two entirely distinct 

 phenomena — (1) the stimulating or actinic 

 effect on the living protoplasm and (2) the use 

 of the energy of the rays to break up carbon 

 dioxide in the chlorophyl-bearing cells. Plant- 

 cells, as a matter of fact, like bacteria, func- 

 tion in absolute darkness, under the bark or 

 in the roots, and do not need the slightest 

 stimulation of light, indeed are killed by it, as 

 a rule. Light is only used to build up the car- 

 bon food, and the cells engaged in this duty 

 are also protected by the green pigment, hairs, 

 etc., but even they are killed by two much 

 light, as the botanists show — each species hav- 

 ing its own danger limit which in the shade- 

 loving plants is a very low one. Indeed, in 

 botanical literature there are increasing num- 

 bers of references to the fact that the effect of 

 light on plant protoplasm is to retard growth; 

 while the efiect on the chlorophyl is to supply 

 carbon food for the cells under the bark. 



It is quite evident, then, that the return of 

 light in the spring starts the phyto-plankton to 

 grow and multiply by furnishing more nutri- 

 tion, but when the light gets so intense that it 

 can penetrate in harmful degree to the proto- 

 plasm, growth is checked. 



Dr. C. Stuart Gager's experiments with 

 radium" are reported to show that in minimal 

 amounts these powerful rays do not penetrate 

 sufficiently to have any effect on the plant 

 protoplasm, but above this minimum and up 

 to an optimum they stimulate all functions. 



' Science, November 26, 1909. 

 ^ Memoirs of the N. Y. Bot. Garden, Vol. IV., 

 1908. 



Beyond the optimum and up to the maximum 

 their effect is a retardation or distortion of 

 function, and beyond the maximum it is 

 lethal. This is precisely the conclusion from 

 the innumerable observations and experiments 

 of the effects of light and ultra-violet on pro- 

 toplasm of animals adjusted to a life in the 

 light — man particularly — though as a matter 

 of fact the stimulation of small amounts of 

 light is not a vital necessity, as shown by the 

 animals which have taken up residence in the 

 deep sea or dark caves or have developed a 

 nocturnal habit. 



Curiously enough, though there are in- 

 numerable observations on the effects of 

 minimal, optimal and maximal amounts of 

 light on the plant as a whole, there are none 

 which differentiate between the effects on the 

 chlorophyl activity and the effects on the 

 protoplasm. The radium rays have no known 

 efiect on the synthesis of the carbon com- 

 pounds — the only rays effective there are 

 small bands in the red or blue or both, and 

 varying with different species. The radium 

 effects are solely due to their influence upon 

 the protoplasm under the bark. On the other 

 hand, the well-known nocturnal growth of 

 plants exposed to electric light is solely due to 

 the increased food synthesis in the leaf, for it 

 is not possible for these rays to penetrate the 

 bark to effect the other cells which constitute 

 the plant and construct its materials. It is so 

 manifestly difScult or impossible to get light 

 to penetrate bark evolved for the very purpose 

 of excluding it, that we probably never shall 

 know exactly how the various intensities of 

 light affect the protoplasm of the higher 

 plants, beyond the one undoubted fact that in 

 amounts sufficient to penetrate thin skins it 

 invariably retards growth or kills. In the 

 case of unprotected unicellular plants, the case 

 is different, and it is known that some species 

 are injured by light in any amount, others 

 seem to thrive best in dim light, while all are 

 injured and killed by an excess, which varies 

 with the species. 



The behavior of phyto-plankton then ac- 

 cording to the light of climate, latitude and 

 season seems to follow aU other forms of 



