. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . zig-zag line (fig. 211 A, E and F). Wittrock stated that inGonatonema ventricosum the spores were formed without any preceding act ofconjugation and he also gave cogent reasons for regarding them as neutraland not as parthenospores. As yet the detailed cytology of the spore-formationin Gonatonema has not been worked out, but as described originally byWittrock (78) in G. ventricosum, and as subsequently observed both in thatspecies and in G. B
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . zig-zag line (fig. 211 A, E and F). Wittrock stated that inGonatonema ventricosum the spores were formed without any preceding act ofconjugation and he also gave cogent reasons for regarding them as neutraland not as parthenospores. As yet the detailed cytology of the spore-formationin Gonatonema has not been worked out, but as described originally byWittrock (78) in G. ventricosum, and as subsequently observed both in thatspecies and in G. Boodlei (W. & G. S. W., 97 A), there is in the early stagesof spore-formation a more or less complete division of the protoplast into twoparts which subsequently fuse together (fig. 211 G). The behaviour of thenucleus during this process may prove to be of great interest and wouldprobably decide whether the spores should really be regarded as aplanosporesor not. It is possible that some are zygospores and others parthenospores, 22—2 340 Conjugate but in the present state of our knowledge they may for the time being beregarded as Fig. 212. Tcmnogametum heterosporum W. & G. S. West. A shows completed scalaviform andlateral conjugation in the same filaments ; B, zygospore formed by scalariform conjugation ;C and D show early stages in the fusion of the gametangia; E is an abnormal case in whichtwo adjacent gametangia were cut off in one filament, one of them having conjugated in ascalariform manner; F, early stage in lateral conjugation; G, completed zygospore. ch,chloroplast; g, gametangium; py, pjrenoid; vg, vegetative cell; zl, zygospore producedby lateral conjugation; zs, zygospore produced by scalariform conjugation. All x455. On the whole it seems highly probable that Gonatonema is specialized and Mesocarpede 341 not primitive. In all its characters it suggests a set back from Mougeotia andin view of the conditions prevailing in M. producta (fig. 211 H
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