UPWARD TRANSLOCATION OF FOODS IN WOODY PLANTS III 
back the food supply was drawn. In all cases starch was present in the 
xylem at the time of ringing. Results obtained when twigs of Crataegus 
were ringed in this way are shown in table 8. 
Table 8, Crataegus sp. Ringed April 8. Measured May 8 
X. Check not ringed. 
A. Ringed in 2nd internode from tip. 
B. Ringed in 4th internode from tip. 
C. Ringed at base of one-year-old wood, usually the 7th or 8th internode. 
D. Ringed back on three- or four-year-old wood. 
Those marked z had half the xylem cut away and three fourths of the phloem. One 
fourth of the phloem was left. 
Lateral buds removed from all. 
A' 
Az 
B 
Bz 
C 
I 
20 
0 
0 
16 
16 
2 
25 
14 
20 
broken 
I 
16 
20 
3 
25 
2 
17 
4 
25 
3 
8 
9 
5.- • 
28 
4 
4 
20 
15 
6 
25 
6 
27 
4 
20 
7 
35 
8 
3_2 
8 
25 
30 
8 
30 
3 
broken 
9 
20 
6 
30 
20 
10 
28 
6 
28 
5 
22 
21 
II 
27 
broken 
broken 
12 
25 
20 
9 
30 
13 
30 
6 
10 
32 
14 
25 
9 
I04 
13 
30 
28 
15 
28 
7 
9' 
13 
18 
16 
30 
12 
84 
16 
25 
17 
30 
30 
9 
10 
20 
Ave 
26.8 
6.1 
26.2 
8.1 
28.0 
17.0 
22.0 
From these results it is apparent that material carried by the phloem 
is necessary for shoot growth. The check in growth cannot be due to any 
injury to the xylem, for if half the xylem is cut away and but a quarter of 
the phloem is left, growth is practically normal. This is shown in the 
columns Az and Bz of table 8 and in figure 2. Two possible explanations 
occur. Either the xylem carries no foods, neither carbohydrates nor nitrog- 
enous material, or the xylem carries certain foods, perhaps carbohydrates, 
while the phloem carries some other substances, possibly nitrogenous, 
which may be necessary for growth. If the second alternative were true, 
the greater the amount of phloem above the ring the greater would be the 
supply of this substance which may act as a limiting factor. The following 
data, however (table 9), offer strong evidence that the carbohydrate supply 
is the limiting factor and that this cannot move upward through the xylem. 
4 These results are not included in the averages, for the wounds were not paraffined 
and the xylem had dried out checking the growth of the shoot. 
