Influence of Sola?- Radiation on Plants. 



65 



is unquestionable, that in the majority of cases, plants after the 

 first stage of their growth require a certain supply of carbonic 

 acid, by the decomposition of which they obtain carbon, setting 

 free oxygen. My brother and I have shown that plants will 

 exist well for a considerable time in an atmosphere devoid of 

 oxygen, for instance in nitrogen, hydrogen, coal-gas, or carbonic 

 oxyd. In order to see the effects of all these atmospheric condi- 

 tions on the germination of wheat and peas, the following experi- 

 ments were made during the latter part of May and the beginning 

 of Jane. 



Six wheat-seeds and six peas were placed on folds of linen 

 floating on mercury, and covered with a colorless glass jar having 

 a capacity of about 20 cubic inches. The linen preserved the 

 seeds from the mercury, and was kept wet by the introduction 

 of a small quantity of water. The jar was full of atmospheric 

 air, and was placed on the table before the window having a SE 

 aspect. After a couple of days or so the peas germinated, and 

 shortly afterwards the wheat. They grew for about a week, and 

 retained a healthy appearance much longer. The experiment 

 was twice performed with similar results, and showed that the 

 arrangement was applicable to the proposed experiments. 



A precisely similar arrangement was made in ajar containing 

 29 cubic inches of hydrogen gas, and having in it a tube con- 

 taining pyrogallate of potash, so as to absorb any trace of oxygen 

 which might be accidentally present in the gas, or might be 

 evolved from the seeds themselves. In four days the swollen 

 peas had begun to burst. They put forth short radicles, but no 

 plume, and in about a week afterwards they were all decaying. 

 The wheat showed no appearance whatever of germination. This 

 experiment was twice performed with the same result. 



Another such arrangement was made in ajar filled with car- 

 bonic acid. Not the slightest appearance was indicated by either 

 the wheat or the peas. They decayed, becoming soft and swollen, 

 and emitted a most offensive smell on the removal of the jar. 



The same was done in a jar filled with common air, and con- 

 taining a solution of caustic potash in a small capsule, so as to 

 remove any carbonic acid which might be given oft by the seeds. 

 In about three days both the wheat and the peas had begun to 

 burst ; four out of the six of each continued to grow for about 

 six days, and remained healthy afterwards. The removal of the 

 carbonic acid, then, did not affect the germination. I subse- 

 quently found that in this experiment I had almost exactly 

 repeated one of Mr. Ellis's in his ' Inquiry into the changes pro- 

 duced on atmospheric air by the germination of seeds,' &c. He 

 employed peas, and satisfied himself that all the oxygen in the 

 jar had been absorbed by the germinating plants. 



SECOND SERIES, VOL. XXII, NO. 64. — JULY, 1856. 9 



