344. A TEXTBOOK OF GENERAL BOTANY 
bacteria, they have definite and highly organized nuclei. Many 
flowering plants lack chlorophyll and live as saprophytes or para- 
sites. These can be distinguished from the fungi by their struc- 
ture, as the flowering plants produce true tissues, have flowers, 
and do not reproduce by means of spores. — 
Many alge are composed of single rows 
of cells and reproduce by spores, but 
they possess chlorophyll. From the fore- 
going it will be seen that the fungi can 
be distinguished by the following three 
characters: the vegetative body is a my- 
celium, they lack chlorophyll, and they 
reproduce by spores. 
The fungi exhibit a great diversity of 
forms and structures. They are divided 
into three subclasses: the Phycomycetes, 
the Ascomycetes, and the Basidiomycetes. 
There are many fungi whose systematic position is uncertain, 
and these are placed together in a group called Fungi Imperfecti. 



Fig. 356. Mycelium of 
Saprolegnia on an insect. 
(X 23 
SUBCLASS PHYCOMYCETES 
This group can be distinguished from other fungi by the fact 
that cross walls are not found in the hyph except when repro- 
ductive cells are produced. Phycomycetes are divided into two 
orders: Odmycetes, reproduced sexually by means of odgonia 
and antheridia, and Zygomycetes, reproduced sexually by the 
fusion. of two similar filaments. 
Saprolegnia. Structure. The Odmycetes are characterized by 
the fact that sexual reproduction is by the fertilization of eggs. 
In order to get an idea of this order we may consider a typical 
example, the genus Saprolegnia. This genus (Fig. 356) grows 
abundantly in water on decaying animal and vegetable matter, 
and sometimes on living animals. It is frequently very destruc- 
tive to fish eggs and young fishes. The vegetative part of the 
plant consists of a branching system of filaments without cross 
