770 



A TEXTBOOK OF THEORETICAL BOTANY 



Anatomy of the Root. 



The primary root is diarch, and secondary thickening is more or less 

 normal as far as is known, except that successive concentric zones of new 

 bundles are formed, which become more definitely circular in arrangement 

 with increasing age. These accessory bundles continue upwards into the 

 hypocotyl and are distributed among the bundles which supply the ridges. 

 This later development of bundle connections in all directions makes the 

 anatomy of the mature plant an inextricable tangle of vascular tissue, con- 

 tinually added to by the ground tissue, which remains meristematic as long 

 as it is alive. 



Anatomy of the Leaf. 



The leaf has parallel venation, like a Monocotyledon, but with side 

 branches which end blindly in the mesophyll as in a Dicotyledon. Each 



% ^^f- 't\ rt'. - "^ 



Vascular bundle 



c ■ ■'r-',^' 





%Sg0''^<>-r^:-J'^......^ * 



Sclereid 



Assimilating tissue 

 Sclerenchyma 



Fig. 770. — Wehvitsc/iia mirabilis. Transverse 

 section of the leaf showing the row of 

 large parallel vascular bundles. 



major bundle is enveloped in a transfusion tissue of tracheid-like cells and 

 has a cambium which increases the bundle tissues by secondary growth 

 (Fig. 770). Around each bundle are also numerous thick-walled fibre cells. 

 The bundles are embedded in a thin-walled parenchyma, which is probably 

 a water storage tissue. There is a well-marked palisade on both sides of the 

 leaf, the epidermis is very thickly cuticularized and the stomata, in parallel 

 rows, are deeply sunken (Fig. 771). Everywhere in the soft tissues are large 

 numbers of lignified sclereids of multifarious shapes, in the walls of which 

 are embedded numberless crystals of Calcium oxalate. 



