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ON THE INFLUENCE OF LIGHT ON THE GROWTH OF PLANTS. 33 
ve 
_ These facts show the importance, amongst many others, of some mode of 
registration by which these ever-varying solar influences may be carefully 
_ observed. There can be little doubt that they exert an influence, sometimes 
i baleful, sometimes beneficial, upon the organized creation, and that we have 
_yet to discover, in these emanations or influences, the secrets of many of the 
_ grand phenomena of the universe. 
. 
Notices on the Influence of Light on the Growth of Plants. 
By Mr. Rosert Hunr. 
THE experiments connected with this very interesting inquiry have been 
steadily pursued, and a concluding report would have been made at this 
_ meeting, but that some experiments, which had been conducted with much 
_ eare, with a view of determining the quantity of solid matter in plants grown 
under different circumstances, were destroyed by the hail-storm which lately 
_ prevailed over an extensive district of the metropolis, the glasses and troughs 
of coloured fluids being broken, and the plants themselves washed into the’ 
soil. As it was impossible to repeat this year these experiments, there was no 
alternative but either to present an imperfect report, or to defer the report 
for another year. The latter course has been chosen, and the detail of 
_ these experiments will be reserved for a future communication ; I have how- 
; ever thought it might be attended with some advantages to state a few of the 
_ leading facts which have been determined. The order of the arrangements 
_ have been the same as those observed in the former experiments, and nearly 
tan the results have been confirmatory of those published six years since. 
__ The germination of seeds is peculiarly due to the influence of the actinic 
or chemical rays; and if these are completely isolated whilst the luminous 
ays are permitted to act upon the soil in which the seeds are planted, no 
_ germination will take place. This influence is exerted and is most necessary 
| up to the point at which the first leaves begin to form, when the luminous 
_ Yays are rendered necessary to effect the formation of woody fibre. It must 
_be remembered that this was a point upon which I was at issue with some 
_ other investigators; and it is due to them that I should state, that the dis- 
‘erepancies between us appear to have arisen from our not observing with a 
sufficient degree of accuracy the point at which the two influences balance 
each other, previously to the more complete exercise of the exciting force 
f light, as distinguished from actinism. The vegetative process having been 
| Carried on until the plant arrives at its maturity, a new agency, the calorific, 
s more decidedly necessary to develope the reproductive functions of the 
| plant; and then, again, the chemical rays combined with the calorific be- 
ome more active than the luminous rays. In spring we find the chemical 
Influences exerting without interference their most decided force: seeds 
then germinate, and young buds and shoots are developed. As soon as this 
is effected, the luminous rays, with the advance of the sun, become more 
ive, and the formation of woody fibre proceeds under their particular 
ency ; not that the chemical power becomes dormant, but it is rendered 
portionally less active by the agency of light. In the late summer and 
autumn the peculiar properties of the calorific rays are required, and 
r their agency, with diminished powers of light, the ripening of fruits 
| and the production of seed are accomplished. 
_ My experiments have also led me to detect some curious influences which 
ap a be due to dissimilar rays, and which in their action exhibit great 
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