THE ROLE OF GREEN PLANTS 



219 



Aiichtor ^ have shown that food and water are not transferred from 

 one side of a tree to the other, but instead that ahnost all of the 

 water taken in is used directly above where it is absorbed, while 

 food passes down from the leaves on the same side of the tree. There 

 is seemingly little cross transfer of food or water in a plant stem. 



Vascular rays must not be confused with the so-called pith rays 

 which are formed in herbaceous stems such as Ranunculus or in the 

 stem of Clematis where, as the primary wood bundles grow in the pith, 

 the pith forms narrow plates between the bundles. These appear as 

 the pith rays in a cross section. 



Conditions of growth upon which the passage of food and water 

 depend differ in monocotyledons from those in dicotyledons. If a 

 stalk of celery or asparagus is placed in red ink over night, the color 

 is seen to be located in little fibrous bundles of tissue which are scat- 

 tered throughout the stem. If such a stained stem is examined in 

 cross section under the microscope, it is found to be made up of pa- 

 renchyma or pith which is dotted with little groups of woody cells 

 of irregular size and shape. These are the vascular bundles which, 



Transverse section of stem of corn, a monocotyledon, showhiK the " scattered " 

 vascular bundles which are cut in cross section. 



■ Auchter, E. C. 

 in Woody Plants?' 



" Is There Normally a Cross Transfer of Foods, Water, and Mineral Nutrients 

 Univ. Maryland .\gric. Exp. Station, Bull. 251, Sept. 1923. 



