752 



A TEXTBOOK OF THEORETICAL BOTANY 



The outstanding feature of the whole stem histology is, however, the 

 presence of vessels, resembling those in Angiosperms. These are formed 



Fig. 753. — Ephedra sp. Transverse section of the stem 

 showing the cortex containing chloroplasts and two 

 of the primary vascular bundles at the margin of 

 the large-celled pith. 



Medullary ray 

 Xylem parenchyma 



Vessel 



Autumn wood 



Fig. 754. — Ephedra sp. Transverse section 

 through the secondary wood of the stem 

 showing the large vessels and the boundary 

 of an annual ring. 



most abundantly, and are individually largest, at the beginning of growth 

 in the spring. They later decrease in size and in numbers and the autumn 



