CLASSIFICATION 71 



minates in twenty-four hours or less, by bursting the membrane and allowing 

 the enclosed protoplast to escape in the form of an amoeboid body, or a 

 zoospore with a single flagellum, which strikingly resembles some of the simpler 

 Flagellata. These zoospores have a single nucleus and one or two contractile 

 vacuoles. They increase in size, and if the conditions are suitable may also 

 multiply by division until their number has greatly increased. Finally they 

 begin to fuse together, at first in small groups, which later grow together into 

 a small plasmodium. In Dictyostelium the separate zoospores never completely 

 fuse, but form a pseudoplasmodium. 



One small group of the Slime-moulds consists of parasites which live within 

 the tissues of living plants. The best-known species is Plasmodiophora brassicce, 

 which infests the roots of cabbages, and produces a serious disease characterized 

 by distorted enlargements on the diseased roots. 



Classification of Myxomycetes 



Professor Macbride (10) gives the following classification of the 

 Myxomycetes : 



A. Parasites, in the cells of living plants. Order 1. Phytomyxinse. 



B. Saprophytes, growing ori decaying vegetable matter. 



a. With free spores. Order 2. Exosporese. 



b. With spores formed in sporocysts. Order 3. Myxogastres. 



Much the greater number of the Slime-moulds belong to the 

 Myxogastres. The Exosporese comprise but a single genus, Cera- 

 tiomyxa, whose affinities are somewhat doubtful. In this genus the 

 plasmodium develops a columnar mass, upon the outside of which 

 are borne small prominences with a spore at the apex of each. 



SUBKINGDOM I. SCHIZOPHYTA 



Leaving aside the Flagellata and Myxomycetes, whose claim to be 

 considered as plants is at least doubtful, the lowest group of genuine 

 plants is the Schizophy ta, Fission-plants, so called because of 

 the formation of cells by fission only. 



Among the Schizophytes are found the simplest known organisms, 

 and there is every reason to believe that they represent the most 

 ancient existing types of living things. 



Cell-structure 



The cell-structure of the Schizophytes has been the subject of 

 many exhaustive studies, but the results of these are by no means 

 uniform, and in spite of the assertions that even the simplest forms 

 show nuclear structures, and other evidences of differentiation, it 

 seems probable that these are wanting in the simpler Bacteria. In 

 the larger forms, e.g. Beggiatoa and the Blue-green Algae, a so-called 

 " Central-body," which may represent a primitive nucleus, is present, 



