GROWING PLANTS UNDER GLASSES OF VARIOUS COLOURS. G3 



was reduced. This means that while vital activities are, so to say, 

 set in motion and enhanced by oxygen, the loss by destructive 

 metabolism is lessened in consequence of a reduced respiration. 



Lastly, experiments conducted at the agricultural experi- 

 mental station at the College of Agriculture, Cornell University, 

 gave the following results* : — 



1. "Very great differences in results may sometimes be 

 expected between samples exposed to light during the process of 

 sprouting and those kept in darkness. 



2. " When such differences occur, they indicate that light 

 retards, or even wholly prevents, germination. 



3. "In some species this influence of light is greatly marked, 

 while in others it is not apparent." 



The few preceding observations will illustrate the difficulties 

 in ascertaining the exact effects of light in germination. They 

 appear to be due to the fact that the several influences of heatt 

 and of each of the rays of the solar spectrum cannot be isolated 

 and studied apart and so ascertained independently of the others, 

 while each species requires a different combination of heat, light, 

 &c. The first broad distinction lies between obscure heat and 

 light, for we all know that heat without light will excite germina- 

 tion, and that it is the most important factor in the process. 

 Now when it is said that certain special colours stimulate 



* Second Annual Report for the Year 18S9, p. 56. The four following 

 examples are given of the percentages of " sproutings " in light and in 

 darkness respectively : Field Poppy, 5G and 74 ; Larkspur, 0 and 20 to 30 ; 

 Adonis aestivalis, 4 and 68 ; Eadishes (1) 91 and 71 ; (2) 82 and 92. 



f The following are results of the influence of heat obtained at the 

 agricultural experimental station, Cornell University {op. cit. p. 40) : — 



1. " Different results are obtained from the same sample of seeds under 

 different variations of temperature, of which the daily mean is essentially 

 the same. 



2. " Sprouting takes place more quickly under an essentially constant 

 temperature of about 74° than under a temperature ordinarily variable, 

 which gives about the same mean. 



3. " Kapidity of sprouting is particularly marked in Beans and Peas. 



4. " As fehe mean temperature becomes lower, rapidity of sprouting 

 hecomes slower. 



5. " Greater rapidity of sprouting does not appear to be correlated with 

 greater percentage of total sprouting. 



6. " Constant temperature, of the degree here mentioned, does not 

 appear to give greater percentages of sprouting ; at least, the variation in 

 this respect between the constant and variable temperatures is no greater 

 than that which is usually obtained from tests conducted under identical 

 conditions. In the seven tests with Beans, however, there is an average 

 gain of 5 per cent, in favour of those under constant temperature." 



