GROWING PLANTS UNDER GLASSES OF VARIOUS COLOURS. 



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M. Pauclion also found that in several cases in which light 

 appeared favourable for the first stages of germination the 

 •temperature happened to be lower. Other observers have also 

 come to the conclusion that light is favourable under similar 

 -conditions of temperature. This, therefore, may be one, if not 

 the chief, use of light in germination with low temperatures. 

 If the preceding considerations are of weight, they will perhaps 

 account for the general results of a more or less equal vegetative 

 activity occurring under the yellow and blue sections of the solar 

 spectrum. 



I will now give some account of my own experiments. They 

 were made in square w T ooden frames w T ith four sides only, of one 

 cubic foot capacity, painted white, within and without. A row 

 of small holes bored obliquely upwards and inwards near the 

 bottom of the front, and similar ones near the top of the back, 

 insured ventilation. The frames were placed on a border of an 

 ordinary kitchen garden, the glasses being laid on the top and 

 facing the south-west. 



The following is a description of the glasses used in the ex- 

 periments, and the quality of the light transmitted, as tested by 

 the spectroscope : — 



As the glasses were all exactly one square foot in area, the 

 same amount of sunlight fell upon each of them, and, with the 

 exception of the yellow T glass, which was one-eighth of an inch, 

 or between three and four millimetres, all the rest were three- 

 fortieths of an inch, or nearly two millimetres in thickness. 



Red*. — Transmitted light appears as an almost purely mono- 

 ■chromatic crimson-red terminating abruptly at d, with a nearly 

 opaque band of very dingy green extending from d to f. The 

 red embraces the position of the very strong chlorophyllian ab- 

 sorption-band No. I, and also the somewhat weaker one, No. II. 



Yellow. — This glass transmits nearly half of the spectrum, 

 from the extreme red up to a point a little beyond f, allowing a 

 -trace of blue to appear. It, therefore, stops the most refrangible 

 half, including the positions of the absorption-bands Nos. Viand 

 VII, if not somewhat of No. V as well. 



Green. — This excludes the red and all the rays of the most 

 refrangible half of the spectrum ; hence it transmits light 



* Sec figure, page 60, for the position of the l'nes A, B, etc. and of the 

 chlorophyll absorption-bands I, II, &c. 



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