60 



Influence of Solar Radiation on Plants. 



Under the obscured yellow glass there were two very similar to, 

 and nearly as large as, those under the obscured colorless. Six 

 others were of the same character, but much smaller ; the roots 

 were very short. The plants in the dark had also grown since 

 the 12th. 



On June 5th the experiments were discontinued. The longest 

 pea-plant under the colorless glass was then only 1'75 inch in 

 length ; the secondary rootlets were remarkably short and thick. 

 The plants under the blue appeared the most healthy ; those 

 under the yellow, whether in full light or obscured, showed con- 

 siderable inclination to send out lateral branches. The stems of 

 the plants in the dark were white, the leaflets were canary -yellow , 

 those which had grown in partial obscurity were also much etio- 

 lated. One of the peas under the obscured yellow had produced 

 a triple stem, and so had one of those under the obscured color- 

 less glass. 



The average length of the roots and stalks of those peas which 

 had germinated under the different solar influences is given in 

 the annexed table : — 





Tap roots. 



Stalks. 



No. of plants- 



Length. 



No. of plants. 



Length. 





10 



1 inch 



10 



1 inch 



Blue, 





2 " ) 

 5 « J 



12 



7 « 



Red, 



11 



35 «• 



11 



6 " 



Yellow 



11 



15 « ) 

 65 " f 



10 



65 « 





10 



2* " 



9 



6 





10 



1-5 " 



10 



5 



Dark, 



12 



3* " 



12 



145 " 



The plants were removed from the bricks and allowed to dry 

 in the air for eighteen hours. The following table shows the 

 increase of weight which had taken place in them during their 

 growth : — 





Original weight 

 of 12 peas. 



No. of plants 

 which had 

 germinated. 



Weight. 



Average 

 weights of 

 each. 



Average in- 

 crease of 

 original weight. 





33 grs. 

 345 " 

 30 " 



34 " 

 355 " 

 31-5 " 

 31-5 " 



10 

 12 

 11 

 11 

 10 

 10 

 12 



54 grs. 

 73 " 

 47 " 

 72 " 

 83 " 

 85 " 

 150 " 



5 "4 grs. 

 61 " 

 43 " 

 6-5 " 

 8-3 " 

 8-5 " 

 12-5 « 



2- 7 grs. 



3- 2 " 

 18 " 

 3-7 " 

 5-4 " 

 59 " 

 99 " 



Blue, 





Yellow, 



Obscured colorless, . . 

 Obscured yellow, . . . 



It being thought that the disproportionate weight of the plants 

 which had grown in the dark might be partially owing to their 

 not having become thoroughly air-dried in eighteen hours, on 

 account of their succulent character, they were exposed in the 



* Very various. 



