CHAP, II.— DIFFERENTIATION OF THALLUS.—COMPOUND SPOROPHORES. 57 
such as Stereum hirsutum, Polyporus zonatus, P. igniarius, P. fomentarius, P. Lenzites 
and their allies. The hymenial side in most of these Fungi increases in circumference 
only as the margin of the pileus continually advances, but no increase in thickness 
is thereby brought about. 
On the other hand there is an addition to the free hymenial surface in every 
period of growth in many species of Polyporus, especially in the Fomentarii of Fries, 
in Polyporus fomentarius for example, P. igniarius and P. Ribis, and in Trametes Pini, 
Corticium quercinum and allied forms. Sections therefore through older specimens 
show zones on the hymenial side as well as in the rest of the tissue of the 
pileus ; each zone answers to a zone in the substance of the pileus and is its con- 
tinuation, the youngest hymenial zone being continued into the outermost marginal 
zone of the pileus. 
Persoon! and Fries? call the zones of these Polypori annual zones. They may 
no doubt be correctly compared in certain points to the annual rings of Dicotyledons, 
but it has never been distinctly proved that only one new zone is formed each year 
in these plants. There is no doubt that many zones are formed in the course of a 
year in most of the other zoned mushrooms. J. Schmitz has shown this in detail 
for Stereum hirsutum, and there are a certain number of many-zoned pilei in the 
Hymenomycetes which only last one year. 
Section XIII. The structure of the mature compound sporophorss either 
continues to be evidently hyphal, or it becomes pseudo-parenchymatous in the sense 
of the word explained in section IV. When a compound sporophore is much 
differentiated both kinds of structure may occur in different regions of it and in 
different strata. 
In the first case the course of the ramification of the hyphae may be quite 
irregular and they may interlace in every direction, as in most sclerotia; this 
happens in sporophores in which the growth is not peripherally progressive, and in the 
small structures mentioned on page 51 in which this mode of growth is at least only 
feebly developed, as in the Uredineae and in endophytic Ascomycetes (Rhytisma, 
Polystigma, Epichloe). The pileus of Morchella and Helvetia may be mentioned 
in this connection. But where the growth is distinctly progressive, whether apical or 
marginal or towards the surface, the great mass of the hyphae usually follow a 
course corresponding to these directions, and in large compound sporophores the 
surface of sections or broken pieces may often appear fibrillate even to the naked eye. 
The course of the hyphae in these cases either corresponds exactly with the form and 
direction of growth of the parts, as for example in Stereum hirsutum (Fig. 23) and in 
the stipes of the smaller Agarics, or the hyphae are sinuous and interwoven with a 
larger or smaller number of ramifications spreading in the most different directions, 
and forming what at first sight appears to be an entanglement of threads, such as we 
see for example in the tissue of the pileus of many Agarics. But sections made in 
the right directions will usually show that here the primary hyphae follow a course 
which answers to the general rule. There are however some exceptions ; a striking 
instance of the latter kind is found in Polyporus annosus°, which has persistent 
progressive growth of the margin of the pileus and of the hymenial projections, yet, 
except in the outermost margin of the latter, the course of the slender interwoven 

1 Essbar. Schwämme, p. 17. 
? Epicris. p. 463. 
® R. Hartig, Zersetzungserscheinungen d. Holzes, p. 21. 
