NON-FILAMENTOUS AQUATIC FUNGI
39
(Section II, A). If these are formed as a result of sexual reproduction
(they are said to be formed sexually in some chytrids and asexually in
others), this fungus will permit utilization of genetic techniques now
prohibited in studies of fungi which display only an asexual life-cycle.
The requirement for acetylglucosamine should prove to be valuable in
looking into the possible role of bicarbonate in chitin synthesis during
morphogenesis (see Section II, F for discussion).
D. Blastocladia
pringsheimii
With Blastocladia, as in the Chytridiales, a motile spore with a single
flagellum begins the ontogenetic series of events which culminate in the
formation of a large and multinucleate cell—the thallus of the organism
—and from which the second generation of spores will be derived. But
here, all superficial resemblance ceases. Long after the discovery of this
organism by Reinsen in 1878, but at least a decade before the report
(Emerson and Cantino, 1948) of Emerson's isolation of
Blastocladia
pringsheimii
in pure culture, it was evident (Lloyd, 1938; Blackwell,
1940) that Blastocladia
displayed great capacity for morphological
variability; its thalli ranged from globose forms, at one extreme,
through somewhat elongated types with main axis terminating in
swollen apices, to cells with various degrees of branching along a much
more slender axis. Later, with pure cultures of B. pringsheimii,
evidence
accumulated quickly that even single spore isolates of the fungus did,
indeed, exhibit great potential for plasticity of form; the range in
variation from globose (Fig. 1, left) to elongated (Fig. 1, right) types was
exhibited repeatedly (Cantino, unpublished notes). These observations
also suggest that supposedly specific differences among members of the
genus (e.g., B. globosa KANOUSE VS. B. pringsheimii
REINSCH; cf.
Sparrow, 1960, p. 680) may have no real basis in fact. But apart from
questions of taxonomy, the organism's capacity to form different thallus
types, together with its capacity to produce both cigar-shaped, thinwalled, colourless sporangia and ovoid, thick-walled, pitted, brown
resistant sporangia (Fig. 1) renders it an ideal subject for morphogenetic
investigations. There is no question that heavy, single-generation
populations of this organism can be grown successfully on solid media,
particularly if precautions are taken to ensure that the substratum has
sufficient buffering capacity to withstand the large quantities of lactic
acid which the fungus is capable of producing. With such cultures, it
should be possible to obtain dense populations of swimming zoospores
by flooding the plants with water, thereby inducing discharge from the
cigar-shaped zoosporangia. Finally, with suspensions of this kind,
massive, agitated, single-generation liquid cultures of Blastocladia can
be started. At the moment, nothing is known about the degree of
39
(Section II, A). If these are formed as a result of sexual reproduction
(they are said to be formed sexually in some chytrids and asexually in
others), this fungus will permit utilization of genetic techniques now
prohibited in studies of fungi which display only an asexual life-cycle.
The requirement for acetylglucosamine should prove to be valuable in
looking into the possible role of bicarbonate in chitin synthesis during
morphogenesis (see Section II, F for discussion).
D. Blastocladia
pringsheimii
With Blastocladia, as in the Chytridiales, a motile spore with a single
flagellum begins the ontogenetic series of events which culminate in the
formation of a large and multinucleate cell—the thallus of the organism
—and from which the second generation of spores will be derived. But
here, all superficial resemblance ceases. Long after the discovery of this
organism by Reinsen in 1878, but at least a decade before the report
(Emerson and Cantino, 1948) of Emerson's isolation of
Blastocladia
pringsheimii
in pure culture, it was evident (Lloyd, 1938; Blackwell,
1940) that Blastocladia
displayed great capacity for morphological
variability; its thalli ranged from globose forms, at one extreme,
through somewhat elongated types with main axis terminating in
swollen apices, to cells with various degrees of branching along a much
more slender axis. Later, with pure cultures of B. pringsheimii,
evidence
accumulated quickly that even single spore isolates of the fungus did,
indeed, exhibit great potential for plasticity of form; the range in
variation from globose (Fig. 1, left) to elongated (Fig. 1, right) types was
exhibited repeatedly (Cantino, unpublished notes). These observations
also suggest that supposedly specific differences among members of the
genus (e.g., B. globosa KANOUSE VS. B. pringsheimii
REINSCH; cf.
Sparrow, 1960, p. 680) may have no real basis in fact. But apart from
questions of taxonomy, the organism's capacity to form different thallus
types, together with its capacity to produce both cigar-shaped, thinwalled, colourless sporangia and ovoid, thick-walled, pitted, brown
resistant sporangia (Fig. 1) renders it an ideal subject for morphogenetic
investigations. There is no question that heavy, single-generation
populations of this organism can be grown successfully on solid media,
particularly if precautions are taken to ensure that the substratum has
sufficient buffering capacity to withstand the large quantities of lactic
acid which the fungus is capable of producing. With such cultures, it
should be possible to obtain dense populations of swimming zoospores
by flooding the plants with water, thereby inducing discharge from the
cigar-shaped zoosporangia. Finally, with suspensions of this kind,
massive, agitated, single-generation liquid cultures of Blastocladia can
be started. At the moment, nothing is known about the degree of