PARENCHYMA TISSUE. 55 



contain dark masses, which, under the high power, are seen to 

 be stellate crystals. 



Make a longitudinal radial section and examine as before. 

 The cork cells look about the same as in cross-section; the 

 collenchyma cells are elongated ; the bast fibres, wood cells and 

 ducts are very much elongated and oblique-ended or tapering. 



Examine cross-sections of other exogenous plants. 



Make permanent mounts of sections stained in ha3matoxylin 

 and fuchsin, also in methyl-green and eosin. 



CHAPTER X. 



PARENCHYMA TISSUE. 



In the parenchymatous series of tissues the cells are less 

 modified, at least in shape, from very young cells than those of 

 other tissues. They mostly retain to maturity the character- 

 istics of the living cell, namely, protoplasm and nucleus and the 

 power to form new cells by division. In some cases they be- 

 come elongated and somewhat fibrous, but more commonly they 

 are not much longer than broad, and have their ends square or 

 rounded rather than oblique or tapering. In most of the tis- 

 sues of the parenchymatous series the cells have thin walls, but 

 in some instances the cell-walls are thickened by cellulose, 

 cutinous or ligneous deposits. 



Ordinary parenchyma or soft ground tissue is the least modi- 

 fied and most abundant of all the plant tissues. The walls are 

 thin and frequently, though not always, composed of unmodified 

 cellulose, commonly spheroidal or polyhedral in form and the 

 longitudinal rarely exceeds the transverse diameter. It in- 

 cludes most of the soft tissues of plants, such as the green cells 

 of the leaf, the cells of pith, a considerable portion of the cells 

 of bark, etc. Sometimes the cell-walls are unequally thickened, 

 so as to present the appearance of markings of various kinds; 

 indeed, they are seldom of uniform thickness, but commonly 

 their membranous character and transparency make them 

 appear so. 



For the study of ordinary parenchyma cells the young 

 Geranium stem, studied in Chapter IX, would serve very well, 

 but for variety sections from the soft green parts of other plants 

 may be taken, such as the petiole of the Begonia, the Pumpkin 

 stem, etc. 



Let cross-sections be examined first in water, then stained 

 with iodine and chlor-zinc-iodine. 



The description of the parts of a typical cell given in Chapter 

 VIII answers very well for parenchyma cells. A structure not 

 noted there is present in all green parenchyma cells, namely, 

 small rounded granules stained deep brown, the chloroplasts or 



