CHAP, II,— DIFFERENTIATION OF THALLUS. —COMPOUND SPOROPHORES. 49 
hymenium or sporogenous layer, and are thus distinguished from the rest of the 
sporophore. At the same time descriptive mycology, following convenience and 
tradition, is in the habit of employing special appellations for the hymenia of the 
several orders and reserving the word hymenium for the Hymenomycetes. 
The structure of the hymenia will be described in later chapters. Many points 
also in the structures and especially in the development of the sporophores, in the 
narrower sense of the word, must be reserved for future consideration, partly because 
a comparative examination of their first inception presupposes a previous discussion of 
sexual relationships, partly because we have frequently to deal with facts which are 
characteristic of single divisions, and which it will be more convenient to discuss when 
we are engaged with these in Division II. Meanwhile it may be well to notice here 
a few phenomena of very general occurrence. 
It is only in certain cases that a compound sporophore begins as a terminal 
or intercalary portion of a single hypha, which portion then developes into its 
ultimate form by successive cell-divisions in every direction and by further differ- 
entiations and growth in definite directions, somewhat after the manner of the anther 
of a Phanerogam, if such a comparison is admissible. Some pycnidia among the 
Pyrenomycetes (see Division II) show this exceptional behaviour. 
The general rule here, as in the development of sclerotia and mycelial strands, 
is that the sporophore proceeds from the union of branches of the hyphae, and grows 
by the elongation and branching of these according to a general plan and in directions 
determined by the species, and that new hyphal branches are introduced between 
those previously formed in agreement with the original design. This earliest stage, 
which may be called the meristematic stage, and in which new segments and new 
hyphal branches are added, is succeeded in every section of the sporophore by a 
stage of increase of volume of the existing elements and of their permanent differentia- 
tion, the amount of which is very different in different cases, and reaches its highest 
point in the Gastromycetes and especially in the Phalloideae. 
The hyphal branches which form the compound sporophore originate in some 
cases in a single branch of the mycelium, which may have the morphological 
significance of an archicarp or homologue of a female sexual organ with its immediate 
supporting structure, as in Eurotium, or have no sexual relationship, as was pointed out 
above in the sclerotia of Coprinus and Typhula variabilis, and in the sporophores of 
some species of Coprinus which were shown by Brefeld especially to be produced 
without the intervention of sclerotia. 
In the majority of better-known cases the formation of the compound sporophores 
begins with the union of two or several or many hyphal branches of different origin. 
This is the case with some of the sporocarps of the Ascomycetes which will be described 
at length in Division II, with the very simple hymeniophore of Exoascus Pruni, with 
most of the compound sporophores mentioned above as growing from sclerotia (the 
various species of Peziza, Claviceps, Typhula gyrans, &c.), and the compound sporo- 
phores of Agaricus melleus whichhave their origin, according to Hartig*, in the mycelial 
strands in the same way as the ordinary mycelial branches. Most of the, Hymeno- 
mycetes which are not fleshy might be added to the list, inasmuch as their compound 

1 1c. above, p. 28. 
[4] E 
