STEMS 57 
a hollow cylinder, but are more or less irregularly scattered, 
as may be seen in a cross-section of a corn-stalk (lig. 56). 
As a consequence, there is no cn- 
closing of a definite pith, nor is 
there any distinetly bounded cor- 
tex. In the bundles there is no 
cambium, and therefore new wood 
and bast cannot be added to the 
old, so that in the trees there is no 
annual increase in diameter; and 
this means that there is no branch- 
ing and no increased foliage from 
‘ Fic. 56.—A corn-stalk, show- 
year to year. <A palm well illus- ing iin schaaszcechione aad 
trates this habit, with its columnar, longitutinal., section: the 
a i scattered vascular bundles. 
unbranching trunk, and its crown 
of leaves, which continue about the same in number each 
year. 
25. Ascent of sap.—The water entering the plant by the 
roots and moving upward through the stem is usually 
called sap. It is not pure water, but contains certain soil 
substances dissolved in it. In low plants, as most annuals, 
the ascent of sap requires no special explanation; but in 
plants such as trees, in which the crown of leaves is many 
feet above the soil, the case is very different. Several 
explanations of the ascent of sap in trees have been sug- 
gested, and all have been disproved, so that we are as yet 
entirely in the dark as to the method. 
That the path of ascent is through the vessels of the 
wood, and not through cortex or bast or pith, may be 
demonstrated by a simple experiment. <A stem of corn 
or sunflower or balsam is cut off and placed in water for 
an hour. Then it is transferred to a vessel containing 
water stained with cheap red ink (a solution of eosin), 
and exposed to diffuse light. A few hours later, sections 
of the stem will show the wood vessels stained red, the 
