31 



taking witli it the fee or reward provided by nature for that special 

 service. 



SOMETIMES THROWN OFF AS SUPERFLUOUS. 



There are, however, occasions when considerable quantities of such 

 matter are thrown off or exuded by the leaves, which effect is taken to 

 indicate an abnormal or unhealthy condition of the plant. At pages 

 106 and 107 of Liebig's boolv (speaking of an experiment made to induce 

 the rising sap of a maple-tree to dissolve raw sugar applied through a 

 hole cut in the bark) he shows that, — 



When a sufficient quantity of nitrogen is not present to aid in 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 ofi 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 ab- 

 sorption of alkalies, we observe the leaves of the lime-tree, and of other 

 trees, covered with a thick liquid containing a large quantity of sugar; 

 the carbon of the sugar must, without doubt, be obtained from the 

 carbonic acid of the air. The generation of the sugar talces place in the 

 leaves, and all the constituents of the leaves, including the alkalies and 

 alkaline earths, must participate in effecting its formation. Sugar does 

 not exude from the leaves in moist seasons, and this leads us to con- 

 jecture 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 pf the honey from plants can in no 

 possible way tend to exhaust the soil or affect its fertility. There is 

 no difierence 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 his views on that point; but there has been no difierence of 

 opinion about the saccharine matter, as to which Liebig's doctrine will 

 be found given unaltered in the latest colonial work on the subject, 

 Maclvor's '" Chemistry of Agriculture," published at Melbourne a few 

 years ago. 



