100 GERMINATION 



With the advent of late Autumn, plant growth, as a whole 

 is checked and there are very few plants which when tested 

 galvanometrically at that season do not yield subnormal 

 deflections. 



Were we discussing a problem affecting animal organisms 

 one could reasonably attribute the phenomena to a deficiency 

 of nerve energy. If we apply the same reasoning to plant 

 life we must, I think, assume that at such times the earth 

 is not giving out the same quantity of current — ^possibly 

 not receiving it — as it does during late Spring, Summer and 

 early Autumn. What is called " forcing " is, after all, 

 little more than a successful attempt to reproduce condi- 

 tions favourable to growth but although a rise of tempera- 

 ture acts as a stimulant in lowering the internal resistance 

 of the plant and of the electrolytes in the soil it has been 

 shown by Dr. Russell and others that such rise must be 

 kept within narrow limits, not only because protoplasm is 

 unable to do more than a certain amount of work but for 

 other reasons. Dr. Russell says: "A slight temperature 

 increase producing a marked increase of growth ; above a 

 certain temperature (which varies somewhat with the 

 conditions the rate of growth falls off ; at higher tempera- 

 tures the plant suffers, the various processes no longer 

 work harmoniously, the protoplasm loses efficiency till 

 finally the plant dies. 



" For purposes of crop production the temperature range 

 is limited by certain secondary effects. If the temperature 

 is too low a purplish pigment appears on the leaf, and the 

 plant grows so very slowly that it is Hable in its early stages 

 to succumb to insect pests . . . and in its later stages 

 to be cut down by Autumn frosts before it has had time 

 to ripen " (low electro-vitality ; "if, on the other hand, 

 the temperature is too high, the plant becomes taller than 

 usual, less robust and, when much water is also supplied, 

 liable to all the fungoid pests that give so much trouble in 

 commercial greenhouses. Only over a comparatively re- 

 stricted range of temperature is it possible to obtain the 

 compact sturdy habit aimed at by the grower," 



