242 Pennington — A Chanico-PJiysiological 



inside the box, and the whole apparatus exposed to bright 

 light, either in a green-house, or, as these experiments 

 were made in the early autumn, in a sheltered place in the 

 Botanic Garden. 



Three screens were used, viz. : blue, green and yellow- 

 orange. These glasses, tested by the spectroscope, were 

 found to allow the following rays to pass: 



/. Blue glass : 



Red, from 738 pp. to 703 pp. 



Yellow-green, 566 pp. to 552 pp. 



Green-blue, blue and violet, 517 pp. to 408 pp. 



2. Green glass : 



Orange, yellow, green and a little blue, from 629 pp. 

 to 458 pp. 



3 . Yellozv-oi'ange glass : 



Red, orange, yellow, green, and green-blue, from 

 687 [i[L. to 464 \jl\l. 



When grown under such conditions, it is obvious that 

 the plant is acted upon by a considerable part of the .spec- 

 trum, since these glasses divide it roughly into three por- 

 tions with much overlapping in the less refrangible rays. 

 Hence the changes observed in the plant are due to a com- 

 bination of forces, these forces being represented by the 

 rays which pass. 



Blue Glass. — The blue light, having a small band of red, 

 some yellow-green, and a little blue-green, in addition to all 

 of the blue and the visible violet rays, acts upon the plant in 

 a much modified form, the red and green tending to over- 

 come the evil effects produced by the blue and violet. As 

 a result of this the plant made a much slower growth than 

 under normal conditions, but a growth far beyond that made 

 under pure blue. 



Starch and sugar diminished in quantity, and frequently 

 the starch disappeared entirely, only to reappear in a short 

 time. The tannin fell considerably below the normal 

 amount, but was never completely lost. The chlorophyll 



