THE PATHOGENIC FUNGI OF PLANTS. 105 



obscure and is replaced by numerous and complex modes of 

 asexual multiplication. 



The lower forms of fungi, in the structure of the thallus, mode 

 of reproduction, and adaptation to an aquatic life, exhibit distinct 

 relationship with the Algae, particularly with the Siphoneae. 



Since the fungi do not possess chlorophyll, their nutrition 

 is carried out by the absorption of organized material in a 

 saprophytic or parasitic manner. Parasitic fungi are the cause 

 of numerous and dangerous diseases of plants, whereas they 

 only rarely bring about a diseased condition of the animal body. 

 Bacteria on the other hand, which cause so many animal diseases, 

 seldom affect plants injuriously. While many parasites are 

 strictly limited to a parasitic mode of life, a large number 

 naturally spend a part of their lives as saprophytes, and others 

 may be made to do so artificially on nutritive substrata 

 under suitable conditions. The latter method forms in fact a 

 valuable aid for completing our imperfect knowledge of the 

 life-histories of parasitic forms. In addition to the well-marked 

 parasitic fungi, there are many saprophytic forms which become 

 parasitic for a relatively short time or imder special conditions 

 of environment. 



The Fungi are divisible into two large groups, the lower" 

 fungi (Phycomycetes) and higher fungi (Mycomycetes). 



The systems instituted by various investigators differ not 

 a little from each other. Three of the principal are : 



De Bart. Zopf. Brefeld. 



(1) Phycomycetes (1) Phycomycetes (1) Phycomycetes 



(2) Ustilagineae (2) Mycomycetes (2) Higher Fungi 



(3) Ascomycetes (a) Basidioraycetes (o) Mesomycetes 



(4) Uredineae (6) Uredineae Hemiasci — Hemibasidii 



(5) Basidiomycetes (c) Ustilagineae (6) Mycomycetes 



(c?) Ascomycetes Ascomycetes — Basidio- 



mycetes 



We shall in the present work consider the Fungi in the 

 following order : 



Lower Fungi or Phycomycetes : 



Chytridiaceae, Zygomycetes, Oomycetes. 

 Higher Fungi or Mycomycetes: 



Ascomycetes. 



Ustilagineae, Uredineae, Basidiomycetes. 



