zygospores (Fig. 55, V. and VI.). The latter are produced in the following manner: Two club-shaped swellings develop on two two neighbouring mycelial threads; these grow towards one another until their ends touch, which then become flat. The two flattened end membranes then coalesce. A septum is then formed in these club-shaped growths, so that an end cell-a copulation cell (Fig. 55, V., c)—and a suspensor (Fig. 55, V. and VI., b) appear. Finally the two end cells melt into one and a zygospore is thus formed (Fig. 55, VI., a). Some species form zygospores easily; with others it seems to be accidental; in short, the conditions of their formation are not yet known. The communications made by Bainier and others on this subject do not hold as regards those species with which the author has experimented.

A third means of propagation is possessed by some species; this consists of the so-called gemmæ or chlamydospores (Fig. 58, a). When the mycelium is immersed in a culture liquid containing sugar, numerous dividing walls make their appearance; short members are thus formed, which swell to a barrel shape and become highly refractive, after which their cell walls thicken. The separate members may grow into mycelium, or develop sporangium carriers at once (Fig. 58, b), or they may separate from one another and increase by budding like yeast cells; the so-called spherical yeast" is thus formed (Fig. 59). The spores

may also behave in this manner.

Hansen has established the following general law for fungi, that the temperature maximum for the development of the organs of propagation lies lower than the maximum for the development of the vegetative organs. This, of course, applies also to the Mucoracea. Not long ago he described two new species, Mucor alpinus and Mucor neglectus, which can both develop zygospores.

He showed

that the temperature maximum for development of sporangia and zygospores is lower than that for development of mycelium, yeast cells and gemma formation, and that the temperature limits for sporangium and zygospore formation change with the species; thus, in Mucor alpinus, sporangium formation has a higher temperature maximum than zygospore formation, whilst for Mucor neglectus the reverse is the case.

(1) Genus: Pin Moulds, Mucor, Micheli.

Characteristic of this order is the ball-shaped sporangium (Fig. 54, III. and IV.) which occurs at the point of the sporangium carrier which is undivided in most kinds, a "columella" separating sporangium and carrier (Fig. 54, III., b). This columella is formed by the more or less vesicular end of the sporangium carrier projecting into the sporangium. A crust of calcium oxalate (Fig. 54, III., c) is often present on the outer wall of the sporangium.

The species belonging to this order live either as saprophytes, i.e., on dead animal or plant matter, or as parasites, i.e., on living organisms. They may be frequently seen as a white, gray or brown felt on dung, bread, fruit, corn, malt, etc., and they also thrive in beer wort. Some species can cause dextrin to ferment, others again contain diastase.

Hansen investigated several of these species with regard to their action on the four sugars: saccharose, maltose, lactose and dextrose. It appeared that lactose is fermented by no species, and saccharose only by one single species after previous inversion, while on the other hand all the species investigated ferment dextrose and maltose. fermentation of maltose proceeds very slowly and only forms higher percentages of alcohol after a relatively long time. Thus, for example, Mucor Mucedo in wort gave after fifteen days at 23° C. only 04 vol. per cent. alcohol; after two and

The

ree quarter months at the room temperature it had formed vol., after six months 3 vol., and after one year only 31 ol. per cent of alcohol.

The fermentability of the various species proved to be very varied. While, for instance, Mucor Mucedo did not

FIG. 54.-Mucor Mucedo, L. I., Spores. II., Germinating spores. III., Sporangium: a, sporangium carrier; b, columella; c, calcium oxalate crystals; d, spores; e, plasma between the spores. (After Brefeld.) IV., a, mycelium with sporangium carriers; s, a bursting sporangium. (After Kerner.)

cent.

reach 4 vol. per cent. of alcohol, M. erectus gave 8 vol. per The facts communicated about alcohol formation in the following are from Hansen.

The powerful yeast fungi of this order show top fermentation phenomena. Emmerling found that, simultaneously with the formation of alcohol during the fermentation, glycerine and succinic acid are formed also in about the same proportion as in Saccharomyces fermentation.

FIG. 55.-Mucor Mucedo, L. V., a, Zygospore formation; b, suspensors; c, copulation cells. VI., A complete zygospore, a; b, suspensors. (After Brefeld.)

The above-mentioned formation of spherical yeast and gemmæ has no connection with the formation of alcohol. Thus M. Mucedo, e.g., yields alcohol without possessing these organs, just as the latter are found in species which have no fermenting power. They are, however, strongly developed in all species of considerable fermenting power.