304 MEDICAL MYCOLOGY 



occur between a mother cell which is still sprouting- and a young daughter 

 cell, in which case the contents of the daughter cell migrate back into the 

 mother cell and form spores. In other species this becomes the rule as in D. 

 mucosus (Sartory, Hufschmitt & Meyer 1930). Debaryomyces frequently oc- 

 curs in cutaneous infections. In Saccharoniyces (Fig. 60) all trace of sexuality 

 has been lost. 



Finally, we should describe a phenomenon whose phylogeny is not clear. 

 It seems to be present in several genera which otherwise do not appear closely 

 related. When Zygopichia Chevalieri of the Pichiaceae is insufficiently nour- 

 ished, 2 ascospores may copulate after they have swollen and ruptured the 

 ascus wall, or an ascospore may copulate with a sprout cell and change to a 

 l-spored ascus, or the ascospore may function without copulation, as an ascus 

 and form more ascospores. In Williopsis Saiurnus, Saccharoniyces ellipsoideus, 

 8. Chevalieri, 8. Mangini, and 8. annulatus, this phenomenon is common. On 

 germination some spores develop the normal sprout mycelium, while others 

 copulate in pairs. The zygote begins to sprout, forming an apparently diploid 

 sprout mycelium in the copulatory canals, occasionally also on the whole sur- 

 face of the copulating cells. Later, Avithout further sexual processes, the asco- 

 spores develop in the vegetative cells. Finally, we have the curious genus 

 Saccharomy codes, whose sole species produces asci with 4 spores which lie in 

 pairs at the two poles (Fig. 63, 1, 2). The spores at a given pole result from 

 the division of one nucleus, thus they are sister cells and are connected by a 

 protoplasmic layer remaining from the periplasm. At germination they swell 

 much in the ascus and form small copulatorj'- canals (Fig. 63, 1-4). Occasion- 

 ally several spores fuse. Two cells of the same sexual tendency attract a 

 third of a different tendency. Copulation may be retarded and the tubes 

 continue to grow, perhaps rupturing the ascus wall. The copulatory processes 

 may fuse with spores from the other pole of the ascus ; or some spores may 

 abort, in which case fusion with spores of another ascus is possible (Fig. 63, 

 9). Very rarely in old cultures, spores may germinate parthenogenetically 

 and develop special strains which continue to reproduce parthenogenetically 

 through several generations at least. After fusion of the copulatory processes, 

 the nuclei migrate into the bridge and fuse (Fig. 63, 5, 7) . Occasionally fusion 

 may occur in one of the spores instead of in the canal or may be retarded 

 and occur only in the germ tube which grows out of the copulatory canal, 

 ruptures the ascus wall, and germinates to a sprout mycelium. Guilliermond 

 (1931) suggests that these forms in which copulation between ascospores 

 occurs, may be derived from the Taphrinaceae where Juel and others observed 

 copulation between sprout mycelium from germinating ascospores. It is un- 

 certain whether this copulation of ascospores has phylogenetic significance, 

 since we find it among widely divergent groups, such as Ascoidea, Williopsis, 

 and Saccharoniyces. In Ascoidea, Walker believes it is purely a vegetative 

 fusion. 



