THIC NATl'Kl-: OF DIATOM MOTION. 123 



toin "in a remarkable manner." Still more cnriously, if 

 grooves were cut in the metal, the power of motion was 

 greater than ever, and the comparatively active motion's of the 

 Rapliidiir are thus parallelled. It is therefore evident, thinks 

 the author, that it is an evolution of gas that produces the 

 motion of the diatom ; and we are told that since motion does 

 not take place in diatoms unless the light is fairly strong, we 

 are arriving at a conception of the true nature of the move- 

 ments in these organisms. The stream of gas, in short, is the 

 oxygen which diatoms give out in daylight like other plant 

 cells. The movement to and fro, we gather, is due to the rel- 

 atively greater expulsion of oxygen in first one and then 

 another half of the cell, owing to the unequal illumination of 

 the two ends. The diatom is supposed by some to proceed 

 fatally toward the light. At this point, however, there is a 

 lack of clearness. How evolving gas at the front end should 

 drive the diatom forward one is at a loss to imagine. How- 

 ever : " The evolving gas seems to act at times as a propellor 

 to push the organism forward and at other times to exert a 

 pulling action to raise the growth on end." 



Mr. Jackson then proceeds to apply the same explanation, 

 /. c, evolution of oxygen, to the movements of the desmids, 

 the CyanphycccT and generally to plant organisms the mecha- 

 nism of motion in which is not obvious. Now it is to be 

 remarked, that the explanation palpably breaks down in the 

 case of Bacillaria paradoxa, and that no such explanation is 

 needed for those blue-green algie that manifestly crawl along 

 painfully like a worm. Kozlowski,'^- in a manner much more 

 systematic and plausible, proposed for explanation, not the 

 evolution of oxygen, but the absorption of carbon dioxide, 

 etc. He supposed that, given a diatom with the two ends 

 unequally illuminated, assimilation would go on more rapidly 

 in the brighter light, and that the inward current would draw 

 the diatom along toward the light source. But it must be 



■■ Ho1;niir;il (^a/.etle, Vol. XXI\'. 



