170 



BACTERIA. FUNGI. 



processes of the parasite fungus pushes out of the cell-cavity of the invaded 

 Spirogyra into the surrounding water again and there swells up into a spherical 

 vesicle, within which the protoplasm divides into eight spores. These spores are 

 then set free as swarm-spores and attack new healthy Spirogyra-cells. 



Materially different is the behaviour of the parasite Ghytridium Ola, which 

 attacks the green cells of fresh-water (Edogonise. Its roundish swarm-spores are 

 furnished each with one long cilium, and swim, searching about in the water until 

 they meet with an OEdogonium-cell to their taste just occupied in the formation of 

 oospores. When they find one, they fasten upon it and send infinitesimally fine 

 hair-like tubes (which have been called rhizoids) into the interior. By means of 

 these tubes they derive their nutriment from the host. The body of the parasite, 

 which remains outside the invaded cell, increases in size, and at length grows out 

 into a sporangium; the latter opens at the top by a lid and once more sets free 

 swarm-spores into the surrounding water. 



Polyphagvbs Euglence, a member of the Chytrideae, is parasitic on the green 

 cells of Euglenae living in water. The swarm spores of this microscopic fungus 

 (see fig. 33*) are oval and furnished, like those of Ghytridium Ola, with a long 

 cilium. They swim about the water with the non-ciliate extremity leading, so that 

 the cilium appears to be a tail at the posterior end. As soon as these swarm-spores 

 have come to rest, they assume a spherical form and send out in all directions thin, 

 hair-like tubes, which search for a host. When a tube reaches an Euglena-cell, it 

 penetrates into the body of the latter, drains it, and, continuing to grow, produces 

 fresh hair-like tubes, which attack other green Euglenae, often linking together 

 dozens of them (see fig. 83^). In this way the Polyphagus grows apace and 

 becomes a comparative large oblong vesicle, whilst the protoplasm within it divides 

 into a number of parts. These, again, turn into swarm spores, with long ciliaiy 

 filaments, and they slip out of the vesicle and may attack fresh Euglenae. 



Curiously enough, even saprophytic water-plants destitute of chlorophyll are 

 sometimes attacked by parasites, and that, indeed, by species belonging to the same 

 group. Thus, for instance, the species of Achlya growing on the dead bodies of 

 fishes and other animals which have perished in the water, are themselves infested 

 by small parasitic Saprolegniacese and Chytrideae. The example of these minute 

 parasites represented in fig. 33 ^ is named Rhizidiomyces apophysatus, and its 

 host is Achlya racemosa. The swarming spores of the parasite lay themselves, 

 in the manner described in previous instances, upon the spherical oogonia of A chlya, 

 and insert extremely fine hair-like tubes into the interior of the cells attacked. 

 These ramify like roots in the Achlya-cells, exhaust them of nutriment, grow 

 perceptibly, and at length form spherical swellings, which, after reaching a certain 

 size, break through the walls of the host-cells, project from the opening, and, 

 lastly, push out in each case a sporangium. The latter produces a number of 

 swarm-spores, which escape into the water and are able to seek fresh prey. 



We cannot here enter into details respecting the other kinds of reproduction 

 occurring in the minute fungi parasitic upon hydrophytes. This is the right place, 



