AUSTRALASIAN BEE MANUAL 159 



sugar applied through a hole cut in the bark) he shows 

 that,— 



When a sufficient quantity of nitrogen is not present to aid 

 m the assimilation of the substances destitute of it, these 

 substances will be separated as excrements from the bark, 

 roots, leaves, and branches. 



In a note to this last paragraph we are told that — 



Langlois has lately observed, during the dry summer of 

 1842, that the leaves of the linden-tree became covered with 

 a thick and sweet liquid in such quantities that for several 

 hours of the day it ran off the leaves like drops of rain 

 Many kilograms might have been collected from a moderate- 

 sized linden-tree. 



And further on, at page 141, he says, — 



In a hot summer, when the deficiency of moisture prevents 

 the absorption of alkalies, we observe the leaves of the lime- 

 tree, and of other trees, covered with a thick liquid contain- 

 ing a large quantity of sugar ; the carbon of the sugar must 

 without doubt, be obtained from the carbonic acid of the air' 

 1 he generation of the sugar takes place in the leaves, and 

 all the constituents of the leaves, including the alkalies and 

 alkaline earths, must participate in effecting its formation 

 bugar does not exude from the leaves in moist seasons, and 

 this leads us to conjecture that the carbon which appeared 

 as sugar in the former case would have been applied in the 

 formation of other constituents of the tree in the event of 

 Its having had a free and unimpeded circulation. 



These quotations will probably be considered sufficient 

 to justify the assertion that the gathering of the honey 

 from plants can In no possible way tend to exhaust the 

 soil or affect its fertility. There is no difference of 

 opinion among scientific men as to the sources from 

 which the saccharine matter of plants is derived. Since 

 Liebig first put forward his views on that subject, as 

 well as with regard to the sources from which the plants 

 derive their nitrogen, the principles of agricultural 

 chemistry have been studied by , the most eminent 

 chemists, some of whom combated the views of Liebig 

 on this latter point (the source of nitrogen and its 

 compounds), and Liebig himself seems to have modified 



