THALLOPHYTA. 619 



single flagellum, or creeps about on a damp substratum ; these motile bodies are the 

 myxamaihce. These amcebae increase at the expense of absorbed nutriment, and 

 undergo repeated division. Ultimately they fuse together into masses of naked 

 protoplasm — the plasmodium-stage — which creep about until spore-formation sets 

 in. The plasmodium is transformed into the reproductive stage, numerous sporangia 

 arising all over its surface. This stage in different cases shows the most varied 

 structure, as may be seen by reference to fig. 367. Either the whole plasmodium is 

 transformed into a single sporangium, as in Lycogala epidendruTn (fig. 367 ^'), or a 

 number of sporangia arise. A portion of the protoplasm becomes hardened to form 

 the wall of the sporangium, whilst the contents is resolved into a mass of dust-like 

 spoi'es. In addition there ai'ises in the majority of forms a sort of internal skeleton, 

 the capillitiwm, which may consist either of a number of elongated tubes with 

 characteristic thickenings on their walls, or these tubes may be united together into 

 a continuous network (fig. 367"). On the bursting of the sporangium the spoi'es 

 are scattered and caiTied away by currents of air. They germinate when they 

 reach a moist substratum, and the life-cycle is passed through anew. Under un- 

 favourable conditions a plasmodium may become encysted, forming a transitoiy 

 resting-stage. If placed in water, the plasmodium escapes from the cyst, and 

 continues its life-history even after a lapse of several months. The substance of 

 the membrane, whether of the sporangial wall, spores, or capillitium, does not seem 

 to consist of cellulose, but rather of a congealed protoplasm. We see, then, that the 

 life-history of a Myxomycete is divided into a nutritive stage consisting of naked, 

 membraneless, protoplasmic masses, and a sporangial, spore-producing stage. In 

 respect of their nutritive stage the Myxomycetes very nearly resemble certain 

 groups of the Protozoa, and on the strength of this resemblance they are regarded 

 by many Botanists and Zoologists as belonging rather to the animal than to the 

 vegetable kingdom. In their manner of reproduction they certainly show analogies 

 to many of the Fungi however. 



Plasmodiophora Brassicce is a parasitic Myxomycete which attacks the roots of 

 the Cabbage, causing the disease known as " Fingers and toes " (c/. p. 522). 



Fossil Myxomycetes are not known. About 450 species have been distinguished. 



Phylum 2.— THALLOPHYTA. 



A large and very heterogeneous collection of plant-forms is included under this 

 term. The word (Greek BaXUs, and <pvt6i') literally means plants with undifferentiated 

 shoots, and includes practically all plants standing below the Mosses and Liverworts 

 in complexity of organization. It is impossible to characterize positively a group, 

 or rather a collection of groups, which shows so wide a range of organization as we 

 find among the Thallophytes. They are often characterized negatively as plants 

 whose bodies show no distinction between axis and appendages (stem and leaves). 

 To such a plant-body the name thallus is given. But though this definition holds 

 good for the great majority of the Thallophytes, yet there are forms (e.g. Bryopsis, 



