THE SPORE-SAC FUNGI . 499 
germinates by forming directly a pseudo-stem which bears a sporan- 
gium soon filled with dust-spores. The formation of zygospores at 
once suggests kinship with alge like Spirogyra, and it is believed 
that molds of the type here shown may have evolved from Chloro- 
phycee similar to the ‘‘pond-scums.” The zygomycetes are fungi 
which produce zygospores. 
181. The water-mold fungi (Class Oomycetes) are typified 
by a small group closely resembling algze because of their aquatic 
habits. These water-molds, as they are called, are well represented 
by species of Saprolegnia (Fig. 327) which grow commonly upon 
dead insects (A) or succulent plant-fragments decaying in water; 
or, in some Cases, as parasites upon fish. As with the bread-molds 
the feeding mycelium is unicellular. Projecting hyphze form ter- 
minal sporangia from which swarm-spores emerge (B,C). Female 
gametangia are formed by swellings on certain hyphe, the protoplast 
becoming transformed into one or more spherical gametes (£). 
Meanwhile, male gametangia develop either from the same hypha 
or from hyphe near by, as club-shaped organs which grow toward 
the female gametangium and send a projection through its wall 
to the gametes within. After fertilization the female gametes be- 
come resistant oospores. These eventually are set free and ger- 
minate by sending out a sporangial hypha in which swarm-spores 
are developed. In some of the water-molds degeneration of the 
sexual reproductive organs has gone so far that, although male 
gametangia are developed no fertilization takes place and oospores 
form non-sexually. In extreme cases oospores are formed although 
no vestige of a male gametangium appears. The life-history of the 
water-molds is essentially similar to that of other o6mycetes which 
are parasitic upon land-plants. All of these fungi, to judge from 
their methods of reproduction are more nearly akin to alge of the 
type represented by Coleochete than to any other we have studied, 
although important differences show that the kinship is rather 
remote. Oomycetes are fungi which produce odspores.  ~ 
182. The spore-sac fungi. (Class Ascomycetes) may be 
illustrated sufficiently for our purpose by the ‘‘ mildews.” 
These, typified by the “powdery mildew” Erysibe, are 
parasitic upon the aerial parts of higher land-plants. As 
shown in Fig. 328 the feeding hyphe creep over the surface 
of a leaf, and at short intervals send out projections into the 
host. These projections by means of which the food is ab- 
sorbed, are called haustoria. Another peculiarity distinguish- 
ing these vegetative hyphe from any previously studied is 
the presence of frequent cross-partitions. Dust-spores are 
1 Haus-tor’i-um < L. haustor, a drinker. 
