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 it in the shape of manures. The saccharine matter, once it 

 is secreted by the plant and separated from it, is even useless 

 as a 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 employed 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. 



