152 BOTANY 



Classification of Fungi (Engler and Prantl, 4) 



The Fungi are divided into three classes, Phycomycetes, As- 

 comycetes, and Basidiomycetes ; the two latter constitute the larger 

 group of the Eumycetes, or True Fungi. 



CLASS I. PHYCOMYCETES 



The Phycomycetes, or Alga-Fungi, include a number of plants 

 which, while not all evidently related among themselves, show more 

 or less affinity with the Green Algse, from which they have probably 

 sprung. A few forms, the Chytridineae, are either unicellular, or 

 produce only imperfect hyphae ; but most of them develop branched 

 hyphae, which are non-septate, like the filaments of the Siphon ese. 

 The Phycomycetes are either saprophytes or parasites, attacking 

 both animals and plants. 



The Phycomycetes are divided into two groups, the Oomycetes 

 and the Zygomycetes, the former showing a difference in the size of 

 the gametes, which in the Zygomycetes are alike. 



SUBCLASS I. OOMYCETES 

 Order I. Chytridineae 



The simplest of the Phycomycetes are the Chytridineae, many of 

 which are aquatics, parasites upon various Algae. Others attack 

 many Flowering Plants, sometimes causing a good deal of damage. 

 A common example of the former group is seen in species of Chytri- 

 dium, one of which, C. olla (Fig. 117, A), often attacks the oogo- 

 nium of various species of CEdogonium. The Fungus produces small 

 uniciliate swarm-spores which on germination send a short germ- 

 tube into the cell of the host. The body of the swarm-spore then 

 develops into a sporangium (sp) within which numerous swarm-spores 

 are produced. At certain times, thick-walled resting-spores are pro- 

 duced, apparently non-sexually, and these in time give rise to new 

 zoosporangia. 



A somewhat more complicated form is the genus Polyphagus. P. Euglence 

 (Fig. 117, C-E) sometimes occurs in great numbers as a parasite upon Eu- 

 glena viridis, whose encysted cells it attacks and destroys. The zoospores of the 

 parasite on germination send out delicate threadlike germ-tubes, which pene- 

 trate the Euglena-cells, and absorb from them their contents (Fig. 17, C). The 

 body of the swarm-spore increases rapidly in size at the expense of the Euglena- 

 cells, and finally sends out a large saclike growth into which the contents pass, 

 and divide into numerous zoospores. In other cases (Fig. 117, F), there is a 

 simple form of sexual reproduction, by which an oogonium and antheridium are 

 formed, the latter fusing with the oogonium, which develops a resting-spore. 

 This, on germinating, develops a zoosporangium, much like that formed from 

 the ordinary zoospores. 



