212 



THE ANATOMY OF WOODY PLANTS 



genus under discussion much more highly magnified. The flanking 

 relation of the transfusion elements to the strand of xylem is now 

 very distinct and recalls that found in the leaves of the Cupres- 

 sineae, Taxineae, etc. Less typical manifestations of the develop- 

 ment of transfusion tissues in the dicotyledons are provided by 

 those forms in which bundles related to stomata exuding fluid 

 water, and consequently known as water-stomata, terminate below 



FIG. 159. Transverse section of leaf of Alnus incana 



the stomatic pores in a mass of wide, short, tracheary elements. 

 This condition, although doubtless derived from ancestral gymno- 

 spermous structure, has departed so far from the original transfusion 

 tissue that it can scarcely be included in the same morphological 

 category. 



Transfusion tissue, as will be apparent from the last paragraph, 

 has become a feature of very subordinate importance in the organi- 

 zation of the leaf in the mass of the dicotyledons. The general 

 structure of the foliar organs in the group may profitably occupy 

 attention at this stage. Fig. 159 reproduces somewhat diagram- 



