CHAPTER I. — HISTOLOGICAL CHARACTERISTICS. o 



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 II). 



The union (Verbindung) of the hyphae to form the compound Fungus-body is for 

 the most part brought about by their mlenveaving (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 1 , ofDaedalea, 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. 

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