GROWING PLANTS UNDER GLASSES OF VARIOUS COLOURS. 79 



three -year-old crowns to violet light associated with dry heat. 

 By these means they flower fourteen days earlier than when 

 treated in the ordinary way. The foliage is somewhat paler 

 when thus forced than is normally the case. 



Although blue light appears from the foregoing observations 

 to have some stimulating effect, the interpretation may be that 

 respiration is somewhat arrested under the more refractive rays 

 of the spectrum, so that assimilative powers are not checked by 

 it. Consequently germinating seedlings and etiolated crowns of 

 the Lily-of-the- Valley may thus grow more quickly than they 

 otherwise would if respiration were more active, which, of course, 

 involves a greater waste of substance. 



With regard to temperature, it is now established that tran- 

 spiration and assimilation are functions of light, and seem to fee 

 almost, if not quite, unaffected by heat ; whereas respiration is 

 powerfully affected by it. Hence, if the temperature is relatively 

 high, we can account for the assimilative powers being defective. 

 More than one observer has noticed that temperature has 

 apparently little or nothing to do directly with the function of 

 assimilation. Thus Famintzin showed that with temperatures 

 ranging from 29° to 39° C. in July 1880, 10*59 cc. of C0 2 were 

 decomposed, while at 20° there were 19*84 cc. Again on 

 August 2, at 13°, 1162 cc, and at 20° there were 19*84 cc. 

 decomposed. Similarly Boussingault found that, when he placed 

 his apparatus at the north side of a great wall exposed to a sky 

 without clouds, the volume of oxygen exhaled did not differ 

 notably from that obtained in direct sunlight. 



These results agree with those obtained from my own experi- 

 ments ; for it will be seen that the largest gain, viz. of plants- 

 grown in the open, is accompanied by the lowest mean tempera- 

 ture. 



Conclusion and Practical Results. 



The net practical results from all the preceding observations 

 appear to be that, first, as far as the preliminary stage of 

 germination, or sprouting of seeds, is concerned, it is for the 

 most part a matter of indifference whether seeds be subjected 

 to light or not ; as in a shorter or longer space of time, to be 

 represented in hours, all that are sound will germinate. 



However, the case of the " Dwarf Rocket " Larkspur opens 

 the question whether there may not be other instances of seeds 



