146 



VEGETABLE PHYSIOLOGY 



are in the spongy tissue which occupies the lower half of 

 the thickness of the leaf (fig. 86). The guard-cells of the 

 stomata, however, always contain them. The green cortex 

 of young stems and twigs also exhibits them. In such 

 plants as the Casuarinas and the Equisetums (fig. 87), in 



t.s. 



FIG. 86. TRANSVERSE SECTION OP PORTION OP THE BLADE OF THE 

 LEAF OF Beta. 



cu, cuticle ; ep, epidermis ; p.pa, palisade tissue ; s.pa, spongy tissue ; 

 v.b, vascular bundle; st, stoma; i.s, intercellular space. 



which the leaves are rudimentary, definite longitudinal 

 bands of cells in the young stems contain them. 



The structure of such a chloroplast as is characteristic 

 of one of the higher plants has not been very completely 

 investigated. There is undoubtedly a protoplasmic basis 

 with which the colouring matter is in some way associated. 



