Notices of Books . 
54i 
of light the author scarcely enters. Nay, in some cases, the few 
remarks which he makes on such subjects are scarcely fairly re- 
presentative of the present state of science. Thus we read : — ■ 
“ The green colour of leaves and the variegated colours of 
flowers exist only under the operation of light. In the dark, 
plants only develop sickly blossoms, like the well-known white 
sprouts of potatoes kept in cellars.” 
The views here expressed are much too sweeping, and require 
to be modified. Thus Dr. Askenasy finds that the influence of 
light upon the colours of flowers varies greatly in different plants. 
The flowers of different varieties of Tulipa Gesneriana , whether 
yellow, scarlet and yellow, or scarlet and white, when grown in 
complete darkness, displayed no constant and appreciable dif- 
ference in colour or intensity from flowers of the same respective 
kinds reared in the full light. The flowers of the common spring 
crocus, both blue and yellow, appeared in their natural colours, 
though not well developed. Upon other flowers, such as a dark 
blue hyacinth, the absence of light was found to produce more 
marked effects. Flowers grown in the light, though at the same 
temperature, were fully a fortnight earlier than such as were 
grown in darkness, and were more intensely coloured. Still the 
latter were not absolutely colourless. Thus it appears that the 
influence of light upon the development of vegetable and animal 
colouring matters, not to speak of other principles, is a subjedb 
which requires much more attention than it has yet received, and 
can by no means be cursorily dismissed. One of Dr. Askenasy’s 
experiments is exceedingly interesting. Portions of the imper- 
fectly coloured flower-spikes of several blue hyacinths, growing 
in the dark, were cut off and placed in glasses of water exposed 
to the full light on the south side of a greenhouse. In a few 
days these flowers had attained as full a shade as those which 
had been reared in full daylight from the first; which proves 
that the development of colour does not depend on a previous 
formation of chlorophyll. 
These deficiencies are the more to be regretted because Dr. 
Vogel, in his Preface, if we do not misunderstand him, complains 
that “ men of science have in great measure negledted this 
subject after the first enthusiasm.” 
On the other hand, some amount of space is taken up with 
matter which might well have been omitted. Thus we find an 
explanation of what is meant by the term “ elements,” which, 
now manuals of chemistry have been multiplied to such an 
extent, can scarcely be regarded as necessary. 
The following passage gives room for reflection : — “ Equally 
peculiar are the changes experienced in sunlight by two other 
elements not so well known, chlorine and bromine, which have 
only been carefully observed latterly.” Chlorine and bromine, 
we should consider, may rank among the best known elements, 
and their combination with hydrogen gas under the adUon of 
