CHAPTER V.—COMPARATIVE REVIEW.—ASCOMYCETES. 225 
4. A richly vegetating primary mycelium or thallus proceeds from the ascospore, 
and its complete development closes with the formation of sporocarps, but as a matter of 
fact it always first produces gonidiophores with gonidia. The germinating gonidia again 
give rise in all cases to a mycelium or thallus of the same qualities and capabilities as 
those which sprang from the ascospore. Here therefore the formation of gonidia 
is not necessary to the development, but it is, as a matter of fact, an invariable 
occurrence. It precedes the formation of sporocarps in the history of the individual, 
and the gonidiophores were therefore often termed the precursors of the sporocarps. 
The formation of gonidia is usually extremely copious in this third category, 
often much more copious than that of the sporocarps, and then generally owing to 
external causes which can be demonstrated; it may be the only mode in which 
the species is propagated during many successive generations, while sporocarps 
appear exceptionally and under special conditions. Some species have more than 
one kind of gonidia, which may then be distinguished according to size as micro- 
gonidia, megalogonidia, macrogonidia, or by special names in particular cases according 
to other characters. 
Again, the gonidia are formed in certain cases on the free surface of the thallus 
on single hyphae or in crowded hymenia; or else in receptacles resembling perithecia. 
These latter have been termed by Tulasne pycnzdza, and the spores or gonidia formed 
in them stylospores—not very happy expressions; the first, however, may be retained 
here, the latter replaced by the words pycnospores or pycnogonidia. 
All known gonidia in the Ascomycetes are acrogenously abjointed after one 
or other of the forms described in section XVI, and none are swarm-cells. 
Examples of species which have been fully examined. The germinating 
ascospore in the Erysipheae (Fig. 107) puts out a short germ-tube, which on a 
suitable substratum, namely the living epidermis of certain Phanerogams, sends first 
of all a haustorium (Fig. 6) into a cell of the epidermis, and then developes into the 
filamentous branched thallus which spreads over the whole surface. Short erect 
branches of this thallus then serially and successively abjoint large colourless 
cylindrico-ellipsoid gonidia, and each of these gonidia yields in germination under 
favourable conditions the same product as the ascospore. Every thallus which 
proceeds from these germinations ends, when it has reached its full development, 
with the production of archicarps and antheridia, that is, of sporocarps. But it need not 
always arrive at this conclusion, but may only form gonidia and propagate itself by means 
of them through an unlimited number of generations. This imperfect development 
may usually be traced to obvious external causes, such as climatic conditions or the 
absence of the nutrient substance required for perfect development, that is, the proper 
species of Phanerogam. The Erysiphe of the grape-vine is the best example of the 
group’. From the circumstances attending its first appearance and its diffusion in 
Europe, it may be safely assumed that it suddenly migrated, and was transferred to 
our vines from some other species of Phanerogam. It most probably came from 
America. In spite of its destructive diffusion over the whole of wine-growing Europe 
the most careful examination has never detected any sign of a sporocarp; the 
invasion was entirely carried out by vast numbers of gonidia, the shape of which 
procured the plant the name of Oidium (O. Tuckeri, Brk.). The sporocarps are 
probably found in N. America on native species of Vitis and described as Erysiphe 
(Uncinula) spiralis, Brk. and Curt., but this is not certain. 

! Beitr. z. Morph. u. Phys. d. Pilze, III, p. 50. 
[4] Q 
