Influence of Solar Radiation on Plants. 



51 



eftee, but stops the chemical, whilst, like the blue, it diminishes 

 greatly the luminous. The yellow again scarcely decreases the 

 illuminating power of light, but almost destroys the chemical 

 action." 



The series of experiments on hyacinths, which was described 

 in the last Eeport, was repeated with additional attention to the 

 effects of partial or complete darkness. The large colorless, blue, 

 red, and yellow bell-glasses were employed, together with a par- 

 tially obscured colorless shade, and a partially obscured yellow 

 shade; and another experiment was instituted under a glass 

 shade placed in a large box, so that the light was completely ex- 

 cluded, except when for a few moments the lid might be removed 

 for the purpose of observing the progress of the experiment* 

 As in the preceding experiment, the bulbs were all of the same 

 description, of a healthy appearance, and of about the same size. 

 After being weighed, they were placed as before on the top of 

 colorless glasses, filled with pure water, and covered with the 

 large bell-jars. In this case the jars were themselves placed upon 

 the perforated boards, with the arrangement of tarlatane, &c, 

 mentioned in the previous paper. The experiments were com- 

 menced on December 10th ; each of them was successful ; the 

 results accorded in some points with those of the former occa- 

 sion, but in other respects there was considerable discrepancy. 

 The experiments made in partial or complete obscurity were per- 

 haps the most instructive. 



Eootlets began to appear immediately under the dark shade, 

 and on December 26th, that is, after sixteen days, they were 

 found to be 1J inch in length, They grew rapidly, and were 

 very numerous. They were thin and long, and appeared to have 

 little strength. Under the obscured colorless and obscured yellow 

 glasses, the rootlets also began to grow quickly, becoming three- 

 quarters of an inch long in a fortnight's time, while under the 

 blue and colorless glass exposed to the full power of the light, 

 the rootlets did not so quickly attain any length, and in the 

 same space of time there was scarcely anything observable under 

 the red or yellow glass. The roots continued to grow under the 

 obscured glasses until the beginning of February, but they 

 arrived more rapidly at maturity under the influence of the 

 white and blue light. Under the red shade the roots never at- 

 tained any considerable length, but they were stout and strong. 

 Under the yellow shade there was scarcely any growth below 

 the bulb until near the end of January, when a few long strag- 

 gling roots made their appearance. This is very accordant with 

 the effect that was observed during the previous season to be 

 produced by the colored glasses. This shows that the develop- 

 ment of the root takes place most rapidly in the absence of all 

 solar radiations ; that partial obscurity is also favorable ; that the 

 less refrangible rays of the spectrum had especial power to 



