382 
PHYSIOLOGY. 
BOOK II. 
water, flowered and ripened seeds; the latter obtained the 
same result with Beans, Onions, and Polygonum tinctorium. 
As light*, if not strictly a vis creatrix, is the great agent by 
which the decomposition, recomposition, and assimilation of 
the juices of plants take place; and as it must be obvious that 
the intensity of the action of vegetable secretions, or their 
abundance, will depend upon the degree of their elaboration ; 
it follows that these must be in direct proportion to the 
quantity of light they have been exposed to. As has been 
observed by the author of the article Botany, in the Library 
of Useful Knowledge, “ We see in practice that the more 
plants are exposed to light when growing naturally, the 
deeper is their green, the more robust their appearance, and 
the greater the abundance of their odours or resins ; and we 
know that all the products to which these appearances are 
owing are highly carbonised. On the contrary, the less a 
plant is exposed to sunlight, the paler are its colours, the 
laxer its tissue, the fainter its smell, and the less its flavour. 
Hence it is that the most odoriferous herbs are found in 
greatest perfection in places or countries in which the sun- 
light is the strongest ; as sweet herbs in Barbary and Pales- 
tine, Tobacco in Persia, and Hemp in the bright plains of 
extra-tropical Asia. The Peach, the Vine, and the Melon, 
also, no where acquire such *a flavour as under the brilliant 
sun of Cashmere, Persia, Italy, and Spain. 
“ This is not, however, a mere question of luxury, as odour 
or flavour may be considered. The fixing of carbon by the 
action of light contributes in an eminent degree to the quality 
of timber, a point of no small importance to all countries. 
“ It is in a great degree to the carbon incorporated with the 
tissue, either in its own proper form, or as resinous or astrin- 
gent matter, that the different quality in the timber of the 
same species of tree is principally owing. Isolated Oak trees, 
fully exposed to the influence of light, form a tougher and a 
more durable timber than the same species growing in dense 
forests ; in the former case its tissue is solidified by the greater 
* For some highly interesting experiments upon the effect of light passing 
through coloured media, in determining the appearance of the lower plants 
and animals, see Morren’s JE'waw sur V Heterogeme dommante ; Liege, 1838. 
