ON THE INFLUENCE OF SOLAR RADIATION ON PLANTS. 15 



On the Influence of the Solar Radiations on the Vital Powers of 

 Plants growing under different atmospheric conditions. — Part III. 

 By J. H. Gladstone, Ph.D., F.R.S. 



During the course of the experiments recorded in my last Report, a number 

 of questions suggested themselves, and were incorporated in my remarks. 

 To the solution of some of these I have since addressed myself. 



In previously examining the germination and early growth of wheat and 

 peas under the various coloured glasses and in obscurity, more or less com- 

 plete, it was thought necessary not to cover the seeds with mould, since that 

 would have greatly interfered with the quantity of the light that surrounded 

 them. For certain reasons also the air was allowed to remain unchanged during 

 the whole vegetation of the plants. A number of well-defined results were 

 obtained ; but they were liable to the objection that the wheat and peas were 

 not grown under normal conditions. I have felt it to be the more necessary 

 to remove this objection, seeing that one of the most important results arrived 

 at was in direct antagonism to what other observers had remarked ; the result 

 ■was, that " the cutting off of the chemical ray facilitates in a marked manner 

 the process of germination, and that both in reference to the protrusion of 

 the radicle, and the evolution of the plume." During the spring of the 

 present year, therefore, another series of experiments was instituted upon the 

 growth of the same plants — wheat and peas — under the same coloured and 

 obscured bell-glasses, with this important difference, that a little garden- 

 mould was placed on the bricks, together with the seeds, but not in sufficient 

 quantity to cover them from the light. The bricks were sunk in the earth 

 of a small garden attached to my residence in London ; the seeds were kept 

 well-watered, and a slight change of air was permitted. The experiment was 

 commenced on April 3. It was thought unnecessary in this instance to keep 

 any record of the weather ; suffice it to say, that the season was generally 

 backward, and that cold east winds prevailed during the latter part of April, 

 which interfered with the growth of the plants materially. Owing most pro- 

 bably to this circumstance, the experiments now detailed were not so suc- 

 cessful as those of the previous year ; the main results, therefore, will only 

 be recorded. 



In respect to the wheat, it began, as before, to germinate most speedily in 

 obscurity, but of the coloured glasses the blue appeared to be the most 

 favourable to its growth ; the red light seemed also advantageous. On 

 May 18th, when the experiment was put an end to, the best developed plants 

 were found under the obscured colourless glass. 



As to the peas, they also grew best and most rapidly in obscurity. Some 

 circumstance militated against their proper development under the colourless 

 and coloured glasses, with the single exception that the roots had been put 

 forth well under the blue glass. On May 18th, it was found that in the dark 

 all the peas experimented with had put forth long roots, and most of them 

 had grown tall plants ; while under the partially obscured colourless and 

 partially obscured yellow glasses, all the peas had grown, giving plants, 

 which for the most part were taller, more succulent and less healthy in 

 colour than those which, having been planted at the same time, had grown 

 in the garden without any covering. The peculiarly beneficial effect of the 

 calorific ray on the growth of peas was not observed in this instance. 



Notwithstanding the imperfect success of this series of experiments, they 

 give support to the view generally entertained of the efficiency of the che- 

 mical ray in facilitat"ing germination, which, however, my previous experi- 

 ments (in accordance with those made by Dr. Daubeny) directly contradict, 



