NUTRITION 
395 
keeping the latter supplied with food) may continue to live for years (fig. 665), 
yet the vigorous growth is above the injury. Girdling experiments with willow 
shoots are often cited as adequate proofs of the conductive function of phloem. 
For example, by removing a ring of cortex 5 mm. wide, 
a few centimeters from the lower end in one case and 
several times as far in another, and placing both shoots 
in water, lateral roots and shoots develop in both cases. 
Their vigor is somewhat proportional to the relative 
lengths of stem below and above the girdling, and this is 
taken to indicate that the new parts can draw only upon 
food stored in the part of the stem above and below the 
girdling, transfer being prevented by the interruption of 
the phloem. But if bridges of bark be left across the 
gap, the differences of development tend to disappear; 
and the more numerous the bridges the less the differ- 
ences. While such experiments agree fairly well with 
other observations, they are in themselves not con- 
elusive, since the results are complicated with obscure 
phenomena of regeneration, and perhaps with wound 
irritability. 
K ? "~ VI 
(4) The content of the sieve tubes, which is a 
coagulable slime, consists more largely of foods 
than would be at all likely unless the sieve tubes 
were organs of either conduction or storage, and 
the latter supposition is unlikely because the 
foods are almost entirely in solution. In a typi- 
cal case analysis showed that, excluding water, FlG - 66 S- Portion of 
,i ... iii the trunk of a pine, the 
the constituents were: carbohydrates, 30 per bark completely destroyed 
cent; amides, 38 per cent; proteins, 20 per cent, by birds at a. A single 
So rich a supply of soluble foods could hardly t^^^Z 
be found anywhere else. (5) A bit of merely than a scantily supplied 
corroborative evidence is derived from the dis- S^tct^owtt 
tribution and relative development of the phloem, especially in the neighbor- 
No plants need more facile movement of foods ho ? of ^ c wound ' but 
lood could not pass a 
than vines, whose stems are necessarily slender freely (perhaps not at all). 
and long, and in none is there better develop- Original in the museum of 
Purdue University. From 
ment of the phloem. Indeed, when the anatomist photograph supplied by 
wishes to study the largest and most specialized STANLEY COULTER. 
sieve tubes, vines are almost invariably selected. Moreover, where the 
requirements for food transfer are the greatest, as in flower clusters and 
in the branches of inflorescences, the phloem strands are particularly 
well developed. 
a 
