i8 BOTANY AND PHARMACOGNOSY. 



The Ascomycetes are distinguished by having a sporangium of 

 a definite shape and size, which is called an ascus, and which 

 contains a definite number of spores, which is two or some multi- 

 ple thereof. The Basidiomycetes are the most highly developed 

 Fungi, producing large fruit bodies, such as are seen in mush- 

 rooms, toadstools and puffballs. They are characterized by pro- 

 ducing spores (basidiospores) on special hyphse. The spores are 

 usual!}- four in number and the spore-producing organ is known 

 as a BASiDiuii. 



PHYCOMYCETES : ALGA-FUNGI.— The plant body of 

 the Phycomycetes consists of a mycelium which is unsegmented, 

 more or less thread-like and sometimes considerably branched. 

 Reproduction takes place by means of several kinds of spores, and 

 by reason of the production of two kinds of sexual spores they are 

 subdivided into two important groups. These are ( i ) the Oomy- 

 cetes which produce oospores, and (2) the Zygomycetes which 

 produce zygospores. 



Saprolegnia. — Probably one of the best representatives of 

 the Oomycetes is the group of water molds known as Saproleg- 

 nia, which are aquatic in their habits and are both parasitic and 

 saprophytic, occurring on living fish, insects, crayfish and decay- 

 ing plants and animals as well. The plant body consists of a 

 mycelium which may be simple or branched, sometimes forming 

 a dense mass (Fig. 11, A). Like the alga Vaucheria, it produces 

 both swarm spores (zoospores) and oospores. The swarm spores 

 (Fig. II, B, C) are produced in sporangia formed by the pro- 

 duction of a partition wall at the end of a hypha. The sporangia 

 are either cylindrical. or spherical, and contain numerous zoospores 

 which have two cilia at one end. These spores are peculiar in 

 that after their escape from the sporangium they swim about, 

 then come to rest and take on a wall, after which resting period 

 they develop two cilia on the side, again move about, and germin- 

 ate when they find a suitable host. 



The oogonia and antheridia (Fig. 11, D-F) are also formed 

 at the ends of hyphse. The oogonia are usually spherical and the 

 wall contains a number of small pores. The contents which are 

 at first more or less uniform, later develop egg-cells, of which 

 there may be as many as fifty in a single oogonium. The anthe- 



