MURRAY ON THE COURSE OF THE SAP. 
5 
function must be performed in the leaf, whence the assimilated 
matter there produced must he transported in some way or other to 
the other parts of the plant in which it is found ; and as these are 
lower down, and some of them even underground, as in the case of 
tubers, that it followed that there must be a descent in some way or 
other, and the prevailing opinion seemed to be that this took place 
by a slow swaying, or wandering motion, by means of endosmose and 
exosmose, through the walls of the cells, which imperceptibly and 
independent of the current of the sap mixed the whole up together, 
or carried the different ingredients to where they were wanted. 
Since I last spoke on the subject I have endeavoured to see if 
actual experiment would throw any light upon it, and as a contri¬ 
bution to its elucidation I have now the honour to submit to the 
Committee the particulars of one or two experiments that I have 
made. 
I made experiments with the Vine, the Fig, the Horse Chest¬ 
nut, and the Hyacinth, but as they all, so far as they went, tended 
in the same direction, I shall speak principally from the Yine, 
which was much more manageable, and more readily took up my 
infusions than any of the others. Thanks to the experiments of 
Professor KcHab and Professor Church, I knew of the virtues of 
lithia as an easily absorbed agent, whose presence could be detected 
anywhere by the spectroscope in however small a quantity it might 
be present, and I had the advantage of Professor Church’s own kind 
assistance in determining for me whether it was present or not. 
As lithia, however, is colourless, I added to my infusions enough of 
litmus to colour them deeply, so that their course might be 
followed directly by the eye, and I am bound to record, as the 
result of my experience, that the lithia told me nothing that 
the litmus did not equally well. The combination of both, no 
doubt, adds to the confidence with which I can trust to my ex¬ 
periments, but the litmus had one great advantage over the lithia 
—that it might be easily handled, and dropped or spilt, without 
interfering with the experiment; whereas with lithia we have 
constantly to be on our guard against any careless dispersal of it— 
as, for instance, by allowing a drop to spill on the bark, or by using 
a knife that has been employed in cutting a portion of a branch 
that has been lithiated to cut one that has not. The form and pro¬ 
portion in which I used the lithia were five grains of citrate of lithia 
to each fluid ounce. To this I added a little glycerine, with the 
view of equalising the specific gravity of the mixture with that of 
the sap, and then as much as I found necessary of small lumps of 
