I2 PASSAGE OF FOOD FROM LEAVES TO STEM. 
from the soil and those absorbed from the air, to be there manu- 
factured into organic substances such as the plant can live upon. 
That the bast tissue is the medium by which the sugar and 
other food stuffs travel from the factories to the seats of con- 
sumption is evidenced from the fact that when the contents of the 
phlem or bast cells are tested they are found to contain the 
same substances as are formed in the leaves, and also that if an 
incision is made round a branch, and a small ring of tissue be 
removed extending inwards as far as the wood, the growing parts 
below the wound dwindle and die, while those above become 
more luxuriant. Thus, though we know where the food stuffs are 
manufactured, by what medium they travel, and their destination, 
yet the exact course followed and the rate of travelling are not 
known, and it was with the view of determining these that the 
following experiments were undertaken. Most of them were 
carried on in the Botanical Laboratory in connection with the 
Technical College, and under the guidance of Professor Scott 
Elliot, to whom I am indebted for suggesting methods of con- 
ducting the experiments, and also for the sympathetic and helpful 
interest which he has shown. 
Several methods were tried, but the following was found to be 
the most successful. The idea was to discover whether it was 
possible to insert a coloured fluid into the food-conducting tissue 
of stems and leaves, and whether the course followed by the food 
material could be studied by the use of such a fluid. 
Both pot plants and cuttings from any available evergreen trees 
and shrubs, such as laurel, rhododendron, pine and box were 
employed. My choice was limited to these, as the experiments 
were made during winter and early spring. 
The method of conducting the experiment was as follows :— 
Eosine was inserted into a puncture made in the stems and on 
the under side of the midribs of the leaves bya fine needle. The 
object is to pierce the bast or phloem only, leaving the xylem or 
wood uninjured. But as the extent of development of cortex, 
bast, and xylem differed in the various stems, and as the dye must 
on no account be introduced into the xylem, it was necessary, first 
of all, to cut and examine a transverse section of each stem in 
order to determine how far to introduce the needle, so that the 
bast would be pierced but the xylem uninjured. After settling 
