June 1900.] BOTANICAL SOCIETY OF EDINBURGH 323 



5. A dilution of the well-known amiDonio-cupric 



sulphate solution, of such a strength as to 

 transmit rays from 400 /iyu. to ooo fi/x, i.e. the 

 violet, blue-violet, bright blue, and green. 



6. A strong solution of the same substance, which 



cut out all the rays except those between the 

 400 fifji and 480 ^/a. 



Under the strong solution of ferric thiocyanate no 

 germination whatever took place within three weeks, 

 though the weak solution allowed the buds to germinate 

 freely ; showing that, while deep red light does not promote 

 germination, the orange and yellow rays are effective in 

 this direction. The strong ammonio-cupric sulphate fluid 

 also prevented germination, while this process took place 

 but slowly in the dilute solution ; showing that, while the 

 violet and deeper blue rays have no effect on germination, 

 the lighter blue, and especially the green, promote this 

 process, though only to a small extent. 



Both potassium bichromate and nickel sulphate allow 

 germination to proceed almost as rapidly as in daylight, so 

 that the yellow and orange rays are apparently the most 

 active, though the green and lower red have also a certain 

 effect, — results which agree closely with those obtained 

 by Forest Heald, who used only strong ammonio-cupric 

 sulphate and potassium bichromate. 



Light is, however, not in itself sufficient, but a 

 certain degree of heat is also essential for germination, and 

 the minimum in this case seems to lie not far below 10° C, 

 as at a lower temperature the buds do not germinate, 

 whatever be the intensity of the illumination to which 

 they are exposed, while the maximum is to be found 

 between 35° C. and 40° C, above which they are rapidly 

 killed. Heat, however, apart from light, is quite incapable 

 of inducing any change in resting buds, as is shown by 

 the following experiments, undertaken with the object of 

 producing germination in darkness by artificial means. 



For this purpose buds were incubated in darkness at 

 temperatures of 25° C, 30° C, and 35° C. for three weeks, 

 but showed at the end of that period no trace of germina- 

 tion, and as exposure to 40° C. for forty-eight hours 

 invariably proved fatal, a temperature higher than 35° C. 



