S18 EXPERIMENTS ON GROWTH BY NIGHT. 



of vegetation at that period of the twenty-four hours, when, 

 from other causes, the powers of digestion and assimilation 

 are suspended. As far as is at present known, that power is 

 heat ; and therefore we must suppose that, to maintain at night 

 in our hot-houses a temperature at all equal to that of the day, 

 is a practice to be condemned. Plants will no doubt lengthen 

 very fast at night in a damp heat, but what is at this time 

 produced seems to be a mere extension of the tissue formed 

 during the day, and not the addition of any new part; the 

 spaces between the leaves are increased, and the plant becomes 

 what is technically and very correctly called "drawn"; for, as 

 has been justly observed, " the same quantity only of material 

 is extended to a greater length, as in the elongation of a 

 wire." 



Some observations made in the garden of the Horticultural 

 Society a few years since place this in a striking light. Certain 

 plants were placed for several weeks in a stove, with a high 

 night temperature — supposed to average 69°: the following 

 were the rates of growth in inches : — 



Night. Day. 



Fig 9.60 .... 9.92 



WiUow .19.08 .... 21.65 



Passionflower 36.20 .... 35.85 



Vine 34.15 .... 34.45 



99.03 101.77 



That is to say, they grew as fast by night as by day, for the 

 apparent difference is obviously unimportant. But when these 

 and other plants were grown in the open air, exposed to the 

 low night temperature of England, the result was wholly differ- 

 ent, as will be seen by the following table : — 



Night. . Day. 



Fig 1.63 .... 6.80 



"WiUow 3.77 .... 9.94 



Hop 42.02 . . . .100.53 



Yine ■ . . . 2.34 .... 4.20 



Scarlet Kunner .'. . .23.11 . . . .97.72 



Jerusalem Artichoke , . 8.23 .... 22.26 



Gourd 21.23 .... 48.05 



102.33 . . . .289.49 



