534 
Notices of Books. 
[October, 
him astray in matters which are determined by weight and 
measure. His experiments, too, are very easily capable of veri- 
fication. Still we are bound to say that his results accord very 
ill with those of other and earlier experimentators. Thus Prof. 
H. Vogel — certainly no mean authority on the chemical aCtion 
of light — states, in his “ Chemistry of Light and Photography ” 
(p. 78), that “ recent observations have established that the 
yellow and red rays, and not the blue and violet, produce the 
greatest chemical effeCt on the leaves of plants.” Dr. R. Hunt, 
in that well-known work the “ Poetry of Science,” fully admits 
that seeds under blue glass will germinate long before others ex- 
posed to ordinary daylight, whilst under the yellow ray the process 
of germination is entirely checked ; but he resumes — “ If the 
experiment is continued it will be found that under the blue 
glass the plants grow rapidly, but weakly, and that, instead of 
producing leaves and wood, they consist chiefly of stalk, upon 
which will be seen here and there some abortive attempts to 
form leaves. When the process of germination has terminated, 
if the young plant is brought under the yellow glass it grows 
most healthfully, and forms an abundance of wood, the leaves 
having an unusually dark green colour, from the formation of a 
large quantity of chlorophyl. Plants do not, however, produce 
flowers with readiness under this medium ; but if, at the proper 
period, they are brought under the red glass, the flowering and 
fruiting processes are most effectively completed.” 
In confirmation Dr. Hunt quotes a letter from Mr. C. Lawson, 
of Edinburgh, an eminent seed-merchant. This gentleman, as 
early as 1853, had proved the value of blue light in accelerating 
germination, and employed it practically in testing the value of 
the seeds coming into his hands in the course of business. He 
found that seeds could be thus caused to germinate in two to 
five days, instead of, as heretofore, in eight to fourteen ; but he 
adds that he has “ always found the violet ray prejudicial to the 
growth of the plant after germination.” 
Here, then, is a complete discrepancy, and either General 
Pleasanton on the one hand, or Messrs. Vogel, Hunt, and 
C. Lawson on the other, must be decidedly mistaken. In all 
such cases the only expedient is further experiment, which in 
this case certainly involves no delicate manipulation, and might 
be satisfactorily performed by any intelligent horticulturist. One 
point of difference between General Pleasanton’s arrangements 
and those of the European experimentators upon the influence 
of the various rays of light upon organic life is, that the latter — 
ourself included — submitted plants and animals to the sole and 
exclusive aCtion of blue, yellow, or red light respectively, whilst 
in General Pleasanton’s experiments the blue light has been 
used mixed in certain proportions with ordinary daylight. 
It appears that the author applied for a patent for his discovery, 
and that Prof. Brainerd was deputed by the Commissioners of 
