Butler.—On Allomyces , $ Aquatic Fungus . 1027 
applied to the exospore and thrown off with the spore, it is visible on 
careful focusing as a thin hyaline third wall external to the others (Fig 13). 
The diagnosis of this Fungus, for which I propose the name Allomyces 
arbuscula , n.g., n.sp., is as follows:— 
Allomyces, n.g. Plant consisting of a large-celled basal body or 
foot, branched above, from which arise the slender fertile filaments; 
filaments septate, branched sympodially or dichotomously, branches termi¬ 
nating in sporangia or resting spores; sporangia single or catenulate, 
ovoid, with several papillae of discharge; zoospores emerging singly, 
without formation of a vesicle, large, oblong or elliptical, i-ciliate, amoeboid 
at first, monoplanetic; resting spores terminal, ovoid, thick-walled, formed 
within the terminal cell of the filament and set free by its rupture, or 
sometimes completely filling it and then thrown off with the terminal cell, 
germination not seen ; membranes of all parts without cellulose. 
Allomyces arbuscula, Butl. Basal body of large cells 100-200 by 
60-100/*, attached below by rhizoids to the substratum, and 
one or more times dichotomously branched above ; fertile filaments 
arising in groups of two or more from the end segments of the 
basal body, septate, cells up to 250 by 15-25 /z, sympodially or less 
often dichotomously branched, each branch terminated by a 
sporangium or chain of sporangia or a resting spore; sporangia 
broad elliptical, or ovoid, 40-70 by 30-40/*, ends bluntly rounded 
or truncate, with one to four papillae of discharge; resting spores 
single, terminal, truncate below, rounded above, with thick brown 
pitted exospore, 40-60 by 30-45/*. 
The affinities of this Fungus must now be considered. The differentia¬ 
tion of the thallus into a dilated basal part and more slender fertile 
branches is a feature common to several genera of the Leptomitaceae 
(Rhipidium , Araiospora, Sapromyces) and also Blastocladia , the position 
of which is doubtful. This basal cell of certain Leptomitaceae is a structure 
which has appealed to all who have studied the group as of great taxonomic 
importance. Nothing like it is known in the other Phycomycetes. Usually 
it is a single cell which may be variously branched or lobed. In Rhipidium 
americanum the branching is more or less dichotomous, and if septation 
were to occur the result would resemble in all essential respects the basal 
body of the new Fungus. The same holds good for Blastocladia to an even 
greater degree. Hence, in spite of the multicellular structure of the basal 
body of Allomyces , it must be held to represent the basal cell of these 
genera. 
The segmentation of the mycelium is a distinguishing feature of the 
Leptomitaceae, including Gonapodya , but not Blastocladia . It is unknown 
in other Phycomycetes except the Ancylistaceae, where every segment - 
