Influence of Solar Radiation on Plants. 53 





Primary weight 

 of bulb. 



Fully devel- 

 oped plant. 



Actual 

 increase. 



" obscured colorless glass. . . . 

 * obscured yellow " 



936 grs. 

 862 " 

 856 " 

 1008 " 

 873 " 

 872 " 

 763 " 



1494 grs. 

 1472 " 

 1438 u 

 1406 " 

 1591 " 

 1556 " 

 1205 " 



558 grs. 

 610 " 

 582 " 

 398 " 

 718 " 

 684 " 

 442 " 



If, instead of observing the actual increase of weight, we 

 compare the original weight of the bulb with that of the fully 

 developed plant, we obtain the following proportions : — 



Under the colorless glass as 1000 : 1596. 



blue " 1000 : 1708. 



" red " 1000 : 1680. 



" yellow " 1000 : 1895. 



" obscured colorless glass as . . . 1000 : 1822. 

 " obscured yellow " ... 1000 : 1784. 

 " dark " ... 1000 : 1579. 



This increase in weight in the growing hyacinth is due to the 

 fixation of water, and not to the decomposition of carbonic acid 

 in the atmosphere ; at least a smaller bulb which was placed 

 under a colorless shade, and cut off from the external atmos- 

 phere by the edges of the glass dipping into water, grew and 

 flowered perfectly well ; and when removed from the shade on 

 March 22d, and dried as the others were, it gave the following 

 weight : — 



Primary weight of bulb. Fully developed plant. Actual increase. 



625 grs. 1167 grs. 542 grs. 



or as 1000 : 1867,— 



a larger proportional increase of weight than in any of the 

 other experiments, the actual increase being about the same as 

 that of the other plant which grew under the colorless glass. 



The leaves that grew in the dark were perfectly etiolated, 

 excepting just at the tips, where they showed the normal green 

 color gradually shading off as it descended. The leaves that 

 appeared in the experiments with the obscured glasses, were 

 somewhat lighter in tint than those growing where the direct 

 radiance of the sun could find access. The character of the 

 light, under which the flowers were grown, did not affect their 

 color at all in the way that might have been expected. They 

 were all, as on the former occasion, of an equally deep purple ; 

 even that which grew in complete darkness exhibited the same 

 depth of color in all the petals, excepting a few of the lower 

 ones. The purple flower under the colorless glass when fading 

 turned to red ; and this was also the case under the blue and 



