CHAPTER I.—HISTOLOGICAL CHARACTERISTICS. 3 
one another through the protuberance, and finally the protuberance is separated 
from the cell on which it first arose by a new wall which usually coincides with the plane 
of the lateral wall. The protuberance generally continues in open communication 
with the second cell, with which it coalesced; but here too subsequent separation 
is sometimes, though seldom, effected by the formation of a wall, and it is only to 
this exceptional case that Hoffmann’s original term ‘clamp-cells’ is properly suited. 
In Coprinus according to Brefeld the first cell, the cell which puts out the 
protuberance, is always the one on the apical side of the transverse wall. In this 
case therefore the whole structure is formed almost exactly in the reverse way to 
that which is suggested by its appearance when fully formed; whether this is so 
in all other cases has yet to be ascertained. 
The growth of the compound Fungus-body, so far as it depends on the 
formation of new cells and not on the expansion of the old, is due simply to the 
growth in length of the united hyphae and to the formation of new branches on 
them; these branches are formed partly on the surface of the body, partly in its 
interior, where they thrust themselves in between the branches previously formed. 
In the fully developed state of these compound forms it is in most cases easy 
to see the fine fibrillation due to their construction out of hyphae; the course of 
single hyphae and their ramifications may often be followed with the aid of the 
microscope for considerable distances, whether they lie parallel to one another or 
whether they cross one another repeatedly and are intertwined. 
In other cases the entire thallus or separate parts of it appear to have an entirely 
different composition. Here the tissue when fully formed consists of isodiametric 
roundish or polyhedral cells, and especially in thin sections no longer appears to be 
an arrangement of hyphae, but resembles the ordinary parenchyma of the higher 
plants. Examples of this tissue are to be found’in the pileus of Russula and of 
Lactarius, in the rind of the peridium in many of the Lycoperdaceae, in many sclerotia, 
in the stipe of the Phalloideae, in many Lichens, and in some other cases. But if we 
examine this tissue more closely and follow the history of its development, we see 
plainly that it is really formed from and consists of hyphae, and that it owes its parenchy- 
matous structure simply to the firm union of the hyphae, and to the form, expansion, 
and displacement of their cells. The parenchyma of the higher plants is formed by 
cell-division, the partition-walls as they successively arise being placed in turns in 
one of three or two directions in space. From this difference in origin the Fungus- 
tissue of which we have been speaking is distinguished by the name of pseudo-parenchyma. 
Successive cell-divisions in two or three directions occur only exceptionally in the 
formation of the thallus of the Fungi, as in pycnidia and perithecia (on this see 
Division IT). 
The non (Verbindung) of the hyphae to form the compound Fungus-body is for 
the most part brought about by their zz/erweaving (Verflechtung) one with another, 
and the direction and closeness of the weft vary according to the species. The 
hyphae of the flocky felt-like tissue of Polyporus fomentarius’, of Daedalea, of the stipe 
and pileus of the Amaniteae, of the medullary layers of many Lichens, &c. are loosely 
woven, leaving broad interstices usually filled with air; those of the firm tissue, often 

1 Amadou of commerce. 
B 2 
