\ BEE MANUAL. 301 
Sir Humphrey Davy had already stated that, “ according to 
the latest experiments of Guy Lussac and Thenard, sugar 
consists of 42°47 per cent. of carbon and 57°23 per cent. of 
water and its constituents.” 
Now Liebig, in several parts of his work, shows that the 
carbon in sugar and all vegetable products is obtained from 
carbonic acid in the atmosphere ; and that ‘“ plants do not ex- 
haust the carbon of the soil in the normal condition of their 
growth ; on the contrary, they add to its quantity.” 
DERIVED FROM THE ATMOSPHERE AND RAIN WATER. 
The same authority shows (as we have already stated in 
Chap. IV.) that the oxygen and hydrogen in these products 
are derived from the atmosphere and from rain water; and 
that it is only the products containing nitrogen (such as gluten 
or albumen in the seeds or grains), and those containing 
mineral matter (silex, lime, aluminium, &c.), which take away 
from the soil those substances that are required to be returned 
to itin the shape of manures. The saccharine matter, once it 
is secreted by the plant and separated from it, is even useless 
asa manure. Liebig says on this head, page 21 :— 
‘The most important function in the life of plants, or, in other words 
in their assimilation of carbon, is the separation, we might almost say 
the generation of oxygen. No matter can be considered as nutritious, 
or as necessary to the growth of plants, which possesses a composition 
either similar to or identical with theirs; because the assimilation of 
such a substance could be effected without the exercise of this function. 
The reverse is the case in the nutrition of animals. Hence such sub- 
stances as sugar, starch, and gum, themselves the products of plants, 
cannot be adapted for assimilation ; and this is rendered certain by 
the experiments of vegetable physiologists, who have shown that 
aqueous solutions of these bodies are imbibed by the roots of plants, 
and carried to all parts of their structure, but are not assimilated ; 
they cannot, therefore, be empioyed in their nutrition.” 
NECTAR OF PLANTS INTENDED TO ATTRACT INSECTS. 
The secretion of saccharine matter in the nectaries of flowers 
is shown to be one of the normal functions of the plant, taking 
place at the season when it is desirable to attract the visits of 
insects for the purposes of its fertilisation. It may then be 
fairly asserted, that the insect, when it carries off the honey from 
any blossom it has visited, is merely taking with it the fee or 
reward provided by nature for that special service. 
