RECENT LITERATURE. 



Heliotropic Animals. 1 — In connection with the work of Prof. 

 E. B. Wilson upon the heliotropism of Hydra, (American Natural- 

 ist, May, 1891,) a brief review of the present paper of Dr. Loeb and 

 some notice of other contributions to the same subject by the same 

 author may not be without interest as pointing out the wide extension 

 of such phenomena amongst animals and their identity with those 

 commonly observed amongst plants. 



The author's thesis is that experiments demonstrate a complete 

 agreement between the movements that animals perform under the 

 influence of light and those that have been demonstrated in plants. 



Following Sachs the heliotropic phenomena of plants are briefly 

 reviewed as follows : 



Stems and roots which bend to or from the source of light until they 

 take the direction of the light, are said to be positively or negatively 

 heliotropic. That this bending is not simply a process of greater 

 growth on the more shaded side is shown by the fact that negatively 

 as well as positively heliotropic plants grow more in the dark. 



That the direction of the light is the determining movement is seen in 

 the actual locomotion of many spores to or from the light. 



The more highly refrangible rays, blue and violet, are the active 

 ones in producing heliotropic movements. 



Movements within a single cell result in the arrangement of 

 chlorophyll bodies with reference to the direction of the incident light 

 and as all plants are to be regarded as a continuously connected set of 

 cells, or as one protoplasmic mass, the true explanation of heliotropic 

 movements may invoke a movement of negative protoplasm away 

 from and of positive protoplasm towards the light. 



In plants, then, light produces an orientation dependent upon its 

 direction and upon its character, wave length, etc., and continues to act 

 a stimulus when of constant intensity. 



A brief survey of the previous work upon heliotropism in animals 

 serves to point out the insignificance of the results achieved. 



Reaumur, 1748, and Trembley, 1791, made direct observations upon 

 the effect of light upon moths and Hydra, but no extensive examina- 

 tion of the subject was attempted. Later Bert, 1869, Lubbock, 1883, 

 and Graber, 1884, made extensive researches into the action of colored 



»Dr. J. Loeb : Der Heliotropismus der Thiere. Wttrzbure, 1890. 



