230 



A YEAR IN SCIENCE 



are not arranged in the form of a hollow cylinder, 

 but are more or less irregularly scattered through 

 the pith. In these stems each vascular bundle has its 

 own cambium layer. 



If the cut ends of any young branches are placed 

 in red ink (a solution of eosin) and left in the sunlight 

 for a few hours and then examined, the red ink will 

 be found to have passed up the stem. In sections of 

 such stems the color wilLbe found in the woody tubes 

 just beneath the bark. This color 

 indicates the path taken by the 

 ascending water. The liquids in 

 trees abandon the inner older wood 

 and move only through the newer 

 wood. This older wood forms the 

 heart wood. 



Liquids entering through the 

 root hairs pass into tubes in the 

 roots. These tubes are continu- 

 ous with those in the wood of the 

 Fig. 97. Longitudi- stem, which in turn join those in 



nal section of a stem Jl ... .. , 



showing the path taken the veins in the leaves, thus lorm- 



by ascending water. 



ing a continuous passageway from 

 the root hairs to the leaves. 



Questions 



1. What is the principal function of stems? 



2. What plants have stems which stand erect? 



3. Name plants which have the climbing habit. 



