60 PARENCHYMA CELLS 



parenchyma cells, fitting closely to one another like the 

 bricks in a wall. 



A parenchyma cell examined in detail (r 1 ) is seen to 

 consist of protoplasm hollowed out internally into one or 

 more cavities or vacuoles (vac] containing a clear fluid. 

 These vacuoles differ from those of Amoeba, Heteromita, or 

 Euglena in being non-contractile ; they are in fact mere 

 cavities in the protoplasm containing a watery fluid : the 

 layer of protoplasm immediately surrounding them is denser 

 than the rest. Sometimes there is only one such space 

 occupying the whole interior of the cell, sometimes, as in 

 the example figured, there are several, separated from one 

 another by delicate bands or sheets of protoplasm. The 

 cell contains a large nucleus (nu) and is completely enclosed 

 in a moderately thick cell-wall composed of cellulose. 



The above description applies to the cells composing the 

 deeper layers of the cortex, i.e., those nearest the woody 

 layer : in the more superficial cells, as well as in the internal 

 cells of a leaf, there is something else to notice. Imbedded 

 in the protoplasm, just within the cell wall, are a number of 

 minute ovoid bodies of a bright green colour (p 2 , ckr). 

 These are chromatophores or chlorophyll corpuscles ; they 

 consist of protoplasm coloured with chlorophyll which can 

 be proved experimentally to have the same properties as 

 the chlorophyll of Haematococcus and Euglena. 



Such a green parenchyma cell is clearly comparable with 

 an encysted Hsematococcus or Euglena, the main differences 

 being that in the plant cell the form is polyhedral owing to 

 the pressure of neighbouring cells and that the chromato- 

 phores are relatively small and numerous. Similarly a 

 colourless parenchyma cell resembles an encysted Amoeba. 



The pith, the epidermis or thin skin which forms the 

 outer surface of herbaceous plants, the greater part of the 



