152 VEGETABLE PHYSIOLOGY 
plants as the Casuarinas and the Hquisetwms (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 Suorion or Portion of AERIAL Stem or AN Equisetum. 
u, cortical lacuna; b, 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 
