152 



VEGETABLE PHYSIOLOGY 



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

 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 



FIG. 87. TRANSVERSE SECTION OF PORTION OF AERIAL STEM OF AN Equisetum. 

 a, cortical lacuna ; 6, lacuna in vascular bundle ; c, chlorophyll-containing cells. 



with which the colouring matter is in some way associated. 

 As already stated, many botanists consider the protoplasm 

 to be arranged in a network, whose meshes are filled with 

 a solution of the pigment. Others consider the protoplasm 

 to be homogeneous, but honeycombed with vacuoles which 

 are filled with the solution of the chlorophyll. Others again 

 think that the pigment forms a layer round the plastid. By 

 the action of dilute acids, or by treating the chloroplasts 



