CHAPTER V. COMPARATIVE REVIEW. ASCOMYCETES. 249 



(/>) Spores with dark brown walls, nonseptate or with one transverse wall, closely 



resembling the spores of No. I in form and size, 

 (f) Brown spores like the last but pluricellular compound, 20-30 p in length and 7-10 /* 



in breadth. 



Each of these spore-forms generally occurs separately in a special receptacle, so 

 that four kinds of pycnidia may be distinguished ; but combinations are also found 

 especially of (a) and (c) in the same receptacle. 

 3. The perithecia. 



The formation of germ-tubes has been observed in all the forms of spores produced 

 in the pycnidia. No other gonidial forms are found in Cucurbitaria Laburni. 



Species of Hypomyces are characteristic examples of the regular formation of two 

 kinds of gonidia ; these plants, like Hyphomycetes, live on the larger Fungi, especially 

 the Hymenomycetes, Hypomyces rosellus for instance, H. chrysospermus, and other 

 species 1 , or on parts of dead plants, as H. Solani on rotten potatos 2 . Besides the 

 perithecia which are comparatively rare, and are always later in their appearance, 

 the mycelium produces 



(1) Microgonidia, comparatively thin-walled and colourless, but tolerably large, ellip- 

 soid, cylindrical, or fusiform unicellular or compoundly pluricellular spores, which are 

 abjointed successively and form small heads at the extremities of the ramifications of 

 verticillately or irregularly branched gonidiophores, and were assigned to the old form- 

 genera Verticillium, Dactylium, Fusisporium, and others. 



(2) Megalogonidia or macrogonidia, sometimes also called chlamydospores, acroge- 

 nously formed and solitary or more rarely appearing a few together one behind another 

 on branches of the hyphae which produce the microgonidia ; their formation generally 

 begins later than that of the microgonidia, from which they are distinguished by 

 their thick membranes, which are often rough with warts and usually coloured, and in 

 most species by their greater size ; they are unicellular or compound pluricellular 

 according to the species. The thickness of their membranes shows that they are 

 adapted to a persistent state of rest. 



Reinke and Berthold have shown that in Hypomyces Solani mycelia are formed from 

 the germ-tubes of both kinds of gonidia as well as of the ascospores, which can again 

 produce both kinds of gonidiophores, and Tulasne's less complete account agrees with 

 theirs. More complete knowledge of the general course of development has not yet 

 been obtained. 



Zopf 's Fumago * may be adduced here in conclusion as an example of a cycle of 

 forms still more copious and varied than that of Pleospora or Nectria ditissima which 

 have already been described. Though Zopf found no ascocarps in his Fungus, yet 

 I place it here with the Ascomycetes, because according to Tulasne 4 the very similar 

 species Fumago salicina has ascocarps, and because we are specially considering 

 at the present moment the Ascomycetes which are not yet quite perfectly known. The 

 species of Fumago are the soot-dew which is found in the form of black fuliginous 

 coatings covering parts of living plants. Zopf studied his plants chiefly in pure 

 cultures on microscopic slides in nutrient saccharine solutions of various degrees of 

 concentration, and ascertained the agreement of the cultivated forms with those which 

 occur in nature. 



I. The mycelium of the Fungus is composed of hyphae with short segments, which, 

 like the cells of the gonidiophores, acquire usually at an early period a brown coloration 

 of the walls accompanied by a gelatinisation of an outer colourless layer, while the 



1 See Tulasne, Carpol. III. 



2 Reinke u. Berthold, as cited on page 245. 



3 Die Conidienfriichte von Fumago (N. Act. Leopold. XL). 

 1 Carpol. II. 



