TISSUES.—PARENCHYMA, 47 
when it will be found that all these organs, however modified in 
form and appearance, are derived originally from one or more 
of the ordinary cells. All the observations made previously, 
therefore, as to the chemical and general] properties of cell-mem- 
brane, as well as to its mode of growth and thickening, apply 
equally to the Vessels. We have already stated this to be the 
case with regard to the Woody Fibres, which we have spoken 
of under the names of Prosenchymatous ,cells and Wood-cells. 
By the combination of the different kinds of cells and vessels, 
we have various compound structures formed which are called 
Tissues ; the most important and the most abundant of tiem 
all is parenchyma, which must therefore be first alluded to. 
1. ParencHyMA.—This is composed of comparatively thin- 
walled cells, whose length comnionly does not exceed their 
Fic. 93. 
Fig. 92. Round or oval parenchyma. In two of the cells a nucleus with a 
nucleolus may be seen. Fig. 93. Stellate or spongiform parenchyma, 
composed of stellate cells with three-cornered intercellular spaces, Fig. 
94, Muriform parenchyma, Fig. 95. Transverse section of the petiole of 
a species of Begonia. e. Epidermis with cuticle above and hypoderma 
below, the latter formed vf collenchymatous cells cl, cl, with thickened 
angles v, v. chi. Chlorophyll granules. p. General parenchyma, below 
hypoderma. After Sachs. 
breadth, or in which the proportion of the two diameters does 
not vary to any remarkable extent. There are several varieties 
of parenchyma, depending chiefly upon the forms of the com- 
ponent cells, and their modes of combination ; the following are 
the more important :— 
a. Round or Oval Parenchyma (figs. 62 and 92).—This is 
formed of rounded, or more or less oval cells, with small spaces 
betweenthem. It commonly occurs in succulent plants, and also 
in those parts where the tissues are of a lax nature. It is 
connected by various transitional forms with— 
b. Stellate or Spongiform Parenchyma, which consists of 
