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 ofAgaricus melleus whichhave their origin, according to Hartig 1 , 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 1. c. above, p. 28. 

 [4] 



