PROTOPLASM AND LIFE. 741 



are restored to the light the starch reappears in the chlorophyl of 

 the cells. 



With this dependence of assimilation on the presence of chlorophyl 

 a new physiological division of labor is introduced into the life of 

 plants. In the higher plants, while the work of assimilation is allo- 

 cated to the chlorophyl-containing cells, that of cell division and 

 growth devolves on another set of cells, which, lying deeper in the 

 plant, are removed from the direct action of light, and in which chloro- 

 phyl is therefore never produced. In certain lower plants, in conse- 

 quence of their simplicity of structure and the fact that all the cells 

 are equally exposed to the influence of light, this physiological divi- 

 sion of labor shows itself in a somewhat different fashion. Thus in 

 some of the simple green algae, such as jSpirogyra and Hydrodictyon, 

 assimilation takes place as in other cases during the day, while their 

 cell division and growth takes place chiefly, if not exclusively, at 

 night. Strasburger, in his remarkable observations on cell-divisions in 

 Spirogyra, was obliged to adopt an artificial device in order to compel 

 the Spirogyra to postpone the division of its cells to the morning. 



Here the functions of assimilation and growth devolve on one and 

 the same cell, but, while one of these functions is exercised only during 

 the day, the time for the other is the night. It seems impossible for 

 the same cell at the same time to exercise both functions, and these 

 are here accordingly divided between different periods of the twenty- 

 four hours. 



The action of chlorophyl in bringing about the decomposition of 

 carbonic acid is not, as was recently believed, absolutely confined to 

 plants. In some of the lower animals, such as Stentor and other infu- 

 soria, the Green Hydra, and certain green planarise and other worms, 

 chlorophyl is differentiated in their protoplasm, and probably always 

 acts here under the influence of light exactly as in plants. 



Indeed, it has been proved* by some recent researches of Mr. 

 Geddes, that the green planarias when placed in water and exposed to 

 the sunlight give out bubbles of gas which contain from forty-four to 

 fifty-five per cent, of oxygen. Mr. Geddes has further shown that 

 these animals contain granules of starch in their tissues, and in this fact 

 we have another striking point of resemblance between them and plants. 



A similar approximation of the two organic kingdoms has been 

 shown by the beautiful researches of Mr. Darwin confirmed and ex- 

 tended by his son, Mr. Francis Darwin on Drosera and other so- 

 called carnivorous plants. These researches, as is now well known, 

 have shown that in all carnivorous plants there is a mechanism fitted 

 for the capture of living prey, and that the animal matter of the prey 

 is absorbed by the plant after having been digested by a secretion 

 which acts like the gastric juice of animals. 



* " Sur la Fonction de la Chlorophyll dans les Planaires vertes," " Comptes Rendus," 

 December, 1878. 



