Plants seem to have an individuality, and often 

 show a decided liking for certain regulations in the 

 use of the light in order to do their best when sub- 

 jected to its influence. 



One would think that plants need the darkness 

 for their well-being, just as animals require the 

 night for sleep and refreshment; but this has been 

 declared by a prominent investigator not to be the 

 case, or at least but to a very limited extent. 

 Under the stimulus of the electric light they keep 

 on growing at night almost as thriftily as in the day- 

 light. What to us would be dissipation and end in 

 disease, seems to them to be profitable pleasure, if 

 the light is properly regulated. Mr. B. F. Thwaite 

 tells us that the leaves of that beautiful plant, the 

 acacia cophanta, which close at night, open almost 

 magically when removed from the darkness into the 

 brilliant beams of the arc-lamp; the leaves nearest 

 the root being the first to be influenced. 



We have been alluding to the effects of the 

 steadily shining arc-light upon vegetation; but if 

 it is flashed at short intervals upon plants it seems to 

 have increased power, at least it will draw the plants 

 more rapidly and strongly toward itself. They 

 seem to be whipped up, as it were, by the violent 

 alternations of intense light and darkness. Helio- 

 tropism is the name given to this effect; it deserves 

 a fuller investigation. 



It is not unlikely that in future experiments, 

 devices will be used to graphically record the 

 progress of the growth of plants. By using the 

 method of M. Mach, one may see plants grow, and 



