ELECTRICITY AND PLANT-GROWING. 55 



they demand a like period of inaetivity. This is particularly true 

 of bulbous plants, and all those which spring from fleshy under- 

 ground parts ; and even with woody greenhouse plants the 

 gardener allows a certain season when the plant is kept in a state 

 of partial inactivity. But this season of "rest" is not a 

 necessary attrilnite of vegetation, as most gardeners think, but is 

 simply an adaptation, and in many cases it can be wholly over- 

 come through long continued cultivation. Some plants modify 

 themselves more readily than others in this respect, due to 

 differences in the elasticity of their organization. If cultivation 

 often overcomes this period of passivity, and thereby proves it to 

 have no necessary vital function, observation of unmolested floras 

 may show it as well, for there are certain regions in which 

 vegetation never ceases to grow ; and, furthermore, the gradation 

 from trees to shrubs and herbs in certain species, or congeneric 

 species, from the south to the north, shows that the duration of a 

 plant may be determined wholly by the seasonal periodicity in 

 which it is placed. This leads me to introduce a phenomenon 

 which is particularly germane to the general subject that I am 

 shortly to bring to your attention — the fact that plants undergo a 

 diurnal variation in function. It is well known that the chief 

 activity of the plant in da^^time is directed towards the getting and 

 making of food, or assimilation, while in the nighttime it uses this 

 food in making growth. ^ But this, again, is only an enforced 

 adaptation or division of labor, for, as the plant cannot assimilate 

 in darkness, it devotes the greater part of its energies at that time 

 to the building of tissiie, and leaves itself free to "make hay 

 while the sun shines." But both these functions may and often 

 do proceed simultaneously ; and in the long days of the Arctic 

 regions plants complete the whole process of growth and fructifica- 

 tion in sunlight. If we once disaltuse our minds of the common 

 belief that plants must rest at night, we shall be prepared to 

 understand that artificial light in the hours of darkness can work 

 no injury unless it carries with it something beside illumination. 



3. Plants are modified by physical manipulation, as training 

 and pruning and the horticultural methods of propagation ; and 



4. By the application of stimuli. The effects of stimuli upon 

 plants are little known, largely because any circumstance which 

 incites unusually rapid growth is commonly classed as a stimulant. 

 But the term should l)e applied to those agencies which appear to 



