302 AUSTRALASIAN 



SOMETIMES THROWN OFP 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 book (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 (in a passage already quoted at page 86) 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 off the 

 leaves like drops of rain. Many kilogrammes 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 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 takes 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 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 amongst scien- 

 tific 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 



