PASSAGE OF FOOD FROM LEAVES TO STEM. 13 
this, a trough of plasticene was formed round each stem about 
four inches above the cut end, or in the case of the pot plants, 
round a branch about three inches from its union with the main 
stem. It is rather more difficult getting the plasticene to adhere 
to the under side of the leaf and to model it so that the eosine will 
not escape, but, with a little care and ingenuity, it can be done. 
To exclude air from the puncture the troughs were first filled with 
eosine, and then the needle was made to puncture the stem from 
above, downwards, at about an angle of 45°. Inserting the needle 
at an angle makes an opening that has several advantages over 
one made at right angles to the stem. For one thing, it holds 
more eosine, and, for another, the injury to the plant is not so 
great. As regards the time allowed, it was found that as the 
eosine was absorbed quicker and travelled more rapidly in the leaf 
midribs than in the stems, less time was required for experiments 
on the former than on the latter. At the end of three or four 
hours the leaves had absorbed sufficient eosine to show definite 
results, whereas at least twenty-four hours had to be allowed for 
stems. After the allotted time, the plasticene was removed, and 
the stems and leaves washed, dried, and set aside for two or three 
hours. This is necessary, for if the sections are cut when the cells 
are flooded with eosine some of it escapes into the adjacent cells, 
and so spoils the result. When cutting the section great care has 
to be taken to disturb the eosine as little as possible. All the 
i transverse sections of the different stems, both those cut at the 
point of insertion of the eosine and others, whether higher up or 
f lower down the stem, showed clearly that the fluid inserted had 
entered the phlcem, diffused from it into the medullary rays of the 
phloem, from these into the cambium, and also into the medullary 
ray cells of the wood. From these latter cells it diffused into the 
water-conducting tissue surrounding the pith. Every precaution 
was taken when cutting the sections, such as cutting towards the 
puncture, keeping the razor and stem as dry as possible, etc., to 
prevent the dye entering the cells which it had not diffused into. 
As a result, it is obvious that it is possible to insert a fluid into 
the bast or phlcem, and that a fluid so inserted is taken up by the 
tissues. 
To determine the course taken by the eosine, longitudinal, as 
OF well as transverse sections, were also taken. From these it was 
Si hl ernie 
ae ee eer re, oe py 
oe = 
oe 
