124 MEDICAL MYCOLOGY 



In the higher Ascomycetes, there are, in addition to the crozier type, a 

 whole series of other developmental forms of ascogenous hyphae which need not 

 concern us at present. 



As far as is known, the further development of the asci is the same in 

 all Ascomycetes. The primary ascus nucleus, which has arisen from the 

 fusion of the dicaryon (Fig. 12, 3), undergoes three divisions, at least one^ of 

 which is meiosis ; the eight daughter cells cut out eight ascospores from the 

 cytoplasm of the ascus by free cell formation. The cytoplasm not included in 

 the spores is called epiplasm, which, besides nourishing the ascospores, pro- 

 vides substances for the sculpturing of the spore walls. In certain forms, the 

 number of nuclear divisions may be limited to two or may increase to sixteen, 

 in the former case producing but 4 ascospores and in the latter 64,936. Where 

 the ascospores are thick-walled, they usually possess a typical germ pore or 

 a meridional fissure. In the latter case, the halves of the ascospore wall sepa- 

 rate in germination like the two valves of a mussel. 



According to the Anglo-Saxon school, represented by Harper, B. 0. 

 Dodge and Gwynne-Vaughan (nee Fraser) the nuclear fusion in the young 

 ascus is not the first and only fusion ; but is preceded by another fusion in 

 the ascogonium directly after plasmogamy. The ascogenous hyphae, accord- 

 ing to this conception, do not contain haploid dicaryons but undivided diploid 

 nuclei which only after the formation of the croziers come together as di- 

 caryons. Because of this double fertilization, the primary ascus nucleus is 

 tetraploid and contains 2x double chromosomes. At the first ascus division 

 (Fig. 12, 4) meiosis occurs with each daughter nucleus containing 2x simple 

 chromosomes. The second step is homeotypic (Fig. 12, 5), the 2x simple 

 chromosomes are halved so that each daughter nucleus still contains 2x simple 

 chromosomes. In the third step (brachymeiosis) (Fig. 12, 6) one-half of the 

 undivided chromosomes migrates to each pole, so that each daughter nucleus 

 of the third division contains x simple chromosomes. 



Although the cytologic reports are somewhat contradictory and in part 

 may be interpreted by either hypothesis, the students of Continental Europe 

 and some in America prefer the interpretation of Dangeard and Claussen. 



First imperfect forms, then sexual organs arise on the haplont. Between 

 these sexual organs plasmogamy occurs, while the male and female nuclei 

 pair as a dicaryon. These dicaryons migrate into the ascogenous hyphae and 

 divide conjugately. The ascogenous hypha thus represents a special diploid 

 phase, the dicaryophase, which ends with caryogamy (fusion) in the young 

 asci. Caryogamy is followed directly by meiosis, usually producing 8 haploid 

 ascospores. In the higher Ascomycetes this scheme of development is further 

 complicated, since the haploid thallus proceeds to form fructifications on or 

 in which the ascogenous hyphae complete their development. As in most red 

 algae and in the sporophyte of the mosses, the dicaryophase is to a certain 

 extent parasitic on the haplont and nourished by it. 



In the simplest case, these fructifications form an undifferentiated mass 

 of tissue, a stroma on or in which the asci are formed. A fructification of this 



