CHAPTER V. — COMPARATIVE REVIEW. — CHYTRIDIEAE. 167 



through the wall of the tube of the Saprolegnia. Each sporangium is the product of a 

 swarm-spore which forces its way into the interior of the tube of the young Saprolegnia, 

 and there lives in amoeboid form in and at the expense of the protoplasm of the tube, 

 and finally after 3-5 days' time is invested with a membrane and becomes a 

 sporangium. The sporangia appear in two forms ; either they are smooth-walled and 

 as soon as their growth is completed produce swarm-cells or else die and disappear; 

 or they have the surface of their membrane beset with delicate spikes and form 

 swarm-cells at once from their dense protoplasm, or first spend a period of at least 

 several weeks' duration as resting-cells, and then produce swarm-cells. The spores 

 of both kinds of sporangia are alike in origin and structure. But the spores 

 formed in the smooth-walled sporangia generally develope into spiky sporangia, and 

 those in the spiky sporangia into smooth ones ; if the conditions are unfavourable 

 to vegetation spiky sporangia are produced in greater numbers than the smooth. 

 Every smooth and every spiky sporangium is formed, as has just been said, directly 

 from a single swarm-spore. Former statements or conjectures to the contrary have 

 not been confirmed by direct and more complete observation. Olpidiopsis fusiformis, 

 which lives in species of Achlya, agrees with O. Saprolegnieae according to A. Fischer 

 in all the details of its history. 



We may consider not only the other parasites of the Saprolegnieae which were 

 placed by Cornu in the genus Olpidiopsis, but A. Braun's Olpidieae also and other 

 forms that are without rhizoids, to be nearly related to those which have just been 

 described ; their affinity is shown by the facts observed, especially the entire absence 

 of rhizoids on the sporangia and the accompanying phenomenon of the resting-cells 

 with spiky membranes. It is not at all easy to see why Cornu separates Olpidiopsis 

 from Olpidium; but this group of species is imperfectly known and needs further 

 investigation. 



Section L. 4. The group of Synchitrieae is marked by the entire absence 

 of rhizoids and by the circumstance that an initial cell proceeding from one swarm- 

 spore breaks up by simultaneous division into a heap (soras) of polyhedric spcran- 

 gial cells which produce swarm-spores. The number of sporangia in a sorus varies 

 from two to more than a hundred. 



The typical forms of this group are gall-forming parasites which live in the 

 epidermal cells of phanerogamous land-plants, where they produce swollen vesicles ; 

 the sporangia which ripen or the resting-cells which germinate if supplied with water 

 burst the membrane which encloses them in order to release the spores or sori, 

 if these have not been previously set at liberty by the decay of their investment. 



Two subordinate groups may be distinguished according to their special course of 

 development, Eusynchytrium and Pycnochytrium, the latter embracing Schroter's 

 ChrysochytriumandLeucochytrium. Pycnochytrium has the simpler development. The 

 swarm-spores which have made their way into the young cells of their host are converted 

 into very large thick-walled resting-cells, one usually in each cell. The resting-spores 

 remain dormant for some time, usually for about a year, and then germinate in the 

 manner shown in Fig. 78 ; the colourless endosporium emerges through a small orifice 

 in the layers of the episporium in the form of a slender papilla, which then slowly 

 developes into a spherical vesicle on the outer surface of the episporium and receives 

 the whole of the fatty protoplasm of the resting-cell (a-c). While the protoplasm 



