26 
HISTOLOGY OF VEGETABLES. 
they are so greatly compressed 
and elongated as to assume the 
appearance of fibres ; many of 
them, as shown in Fig. 18, are 
seen to bifurcate; but a trans- 
verse line, indicating the cell- 
wall, is occasionally visible. 
Another variety of cell ar- 
rangement is known as the 
muriform, from its resemblance 
to that of bricks in a wall ; it forms the medullary 
rays of most woods, and gives to them the peculiar 
appearance known as the silver grain ; such cells are 
readily seen in the Conifera?. 
Other forms, especially the sinuous, occur in the 
cuticle of most plants ; the cylindrical, however, is best 
seen in the Characeee. 
From the form and structure of cells, we proceed to 
consider the nature of their contents ; these are colour- 
ing matter, starch, oil, raphides, silica, &c. I have 
already stated, that the beautiful variety of colours seen 
in the corollse of flowers is dependent, not upon the 
membrane composing the cells, but upon colouring 
matters, usually of a fluid nature, contained within 
them. The cells of the cuticle of the common garden 
Rhubarb afford an excellent illustration of this fact; 
some of them filled with a red coloured fluid occurring 
singly among others destitute of colouring matter. In 
the corolla of a Pelargonium , most of the cells are full 
FIG. 18 . 
Elongated cells of Boletus ig- 
niarius. 
