36
EDWARD C. CANTINO AND JAMES S. LOVETT
culture in the laboratory. Much has been done already with them and,
no doubt, much more is bound to come.
Before we focus attention on the model system of our choice, it would
be well to consider briefly several organisms with which sufficient work
has been done to suggest that the future holds much promise for them
as vehicles for experimental studies of differentiation; a species of
Ehizidiomyces
in the Hypochytriales, a species of Karlingia
and
Rhizophlyctis
rosea in the Chytridiales,f and Blastocladia
pringsheimii
and Blastocladiella britannica in the Blastocladiales, all of which display
a determinate system of growth.
A. Rhizidiomyces sp.
Judging from the inherent, overall simplicity of its short life-history,
and from what has been accomplished with it so far,
Ehizidiomyces
promises to be a good subject for developmental studies. Starting with
an anteriorly uniflagellated spore, it first 'loses' (Fuller, 1962), whether
it retracts it or discards it is apparently not clear, its flagellum and then
commences to enlarge. During the nuclear divisions which ensue, nuclear
membranes apparently persist; they seem to constrict between two
poles immediately before the daughter nuclei are formed, in a fashion
similar to that described some years ago (Turian and Cantino, 1960) for
another aquatic fungus, Blastocladiella
emersonii. Ultimately, there is
evolved a globose and multinucleated cell, many-fold greater in size than
the original spore, to which a rather simple system of rhizoids is
attached. This coenocytic protoplast is then released—essentially in
toto—through
a discharge tube ; it does not simply float away however,
but remains attached to the now-empty parent cell. Finally, this
protoplast is segmented by cleavage planes, and then cell walls, into a
population of spores; the latter are released upon dissolution of the
vesicular membrane, and the process is begun again.
By growing microcultures of this fungus attached to submerged
cover-slips to which (like Blastocladiella; Turian and Cantino, 1960) they
stick tenaciously as if glued thereto, Fuller has established a system
which deserves to be—and, we can assume, will be—exploited further.
The sparkling photographic documentation (Fuller, 1962) of the last
f In singling out these organisms, we do not mean to ignore the true chytrid Rhizophydium. Not only is the genus Rhizophydium the largest and the most complex among
the chytrids, but the many characters so far described for members of its brood '. . . are
usually found, upon careful investigation of a great many individuals, to be subject to
wide variation' (Sparrow, 1960). Now, with some knowledge of its nutrition (Goldstein,
1960b) and the composition of its wall material (Aronson and Preston, 1960) already
available, members of this genus should prove to be valuable tools for experimental
studies of morphological plasticity, and they should serve, as well, in the cause of experimental taxonomy.
EDWARD C. CANTINO AND JAMES S. LOVETT
culture in the laboratory. Much has been done already with them and,
no doubt, much more is bound to come.
Before we focus attention on the model system of our choice, it would
be well to consider briefly several organisms with which sufficient work
has been done to suggest that the future holds much promise for them
as vehicles for experimental studies of differentiation; a species of
Ehizidiomyces
in the Hypochytriales, a species of Karlingia
and
Rhizophlyctis
rosea in the Chytridiales,f and Blastocladia
pringsheimii
and Blastocladiella britannica in the Blastocladiales, all of which display
a determinate system of growth.
A. Rhizidiomyces sp.
Judging from the inherent, overall simplicity of its short life-history,
and from what has been accomplished with it so far,
Ehizidiomyces
promises to be a good subject for developmental studies. Starting with
an anteriorly uniflagellated spore, it first 'loses' (Fuller, 1962), whether
it retracts it or discards it is apparently not clear, its flagellum and then
commences to enlarge. During the nuclear divisions which ensue, nuclear
membranes apparently persist; they seem to constrict between two
poles immediately before the daughter nuclei are formed, in a fashion
similar to that described some years ago (Turian and Cantino, 1960) for
another aquatic fungus, Blastocladiella
emersonii. Ultimately, there is
evolved a globose and multinucleated cell, many-fold greater in size than
the original spore, to which a rather simple system of rhizoids is
attached. This coenocytic protoplast is then released—essentially in
toto—through
a discharge tube ; it does not simply float away however,
but remains attached to the now-empty parent cell. Finally, this
protoplast is segmented by cleavage planes, and then cell walls, into a
population of spores; the latter are released upon dissolution of the
vesicular membrane, and the process is begun again.
By growing microcultures of this fungus attached to submerged
cover-slips to which (like Blastocladiella; Turian and Cantino, 1960) they
stick tenaciously as if glued thereto, Fuller has established a system
which deserves to be—and, we can assume, will be—exploited further.
The sparkling photographic documentation (Fuller, 1962) of the last
f In singling out these organisms, we do not mean to ignore the true chytrid Rhizophydium. Not only is the genus Rhizophydium the largest and the most complex among
the chytrids, but the many characters so far described for members of its brood '. . . are
usually found, upon careful investigation of a great many individuals, to be subject to
wide variation' (Sparrow, 1960). Now, with some knowledge of its nutrition (Goldstein,
1960b) and the composition of its wall material (Aronson and Preston, 1960) already
available, members of this genus should prove to be valuable tools for experimental
studies of morphological plasticity, and they should serve, as well, in the cause of experimental taxonomy.