OLIVE : MONOGRAPH OF THE ACRASIEAE. 
493 
of the Physaraceae possess stalks, each composed of a column of 
cells surrounded by a mucous sheath,— conditions which may be 
compared with those in the stalks of the Acrasieae. 
Morphologically, therefore, the plasmodium cannot be assumed to 
have been derived from the pseudoplasmodium, since there are no 
evident resemblances between the two and consequently the Acra¬ 
sieae and the Myxomycetes may be regarded as related only through 
the Amoebae, with which their mvxamoeba condition indicates 
undoubted relationship. While, in drawing this conclusion, there 
may seem to be danger of interpreting lack of analogy as lack of 
homology, it is nevertheless difficult if not impossible to conceive 
of a near relationship between twm such diverse structures, whose 
morphological as well as physiological differences are so apparent. 
The facts, therefore, seem to indicate that instead of having but one 
series of organisms forming one genetic line, as believed by de Bary 
and other writers, we have two distinctly divergent and genetically 
independent series which may have had a common origin. 
Zopf (’ 92 ) has suggested that the Labyrinthuleae may form in 
some respects a link intermediate between the Acrasieae and the 
Myxomycetes. To uphold this view, Zopf regards the net-plas- 
modium of the Labyrinthuleae as the homologue of both the 
pseudoplasmodium and the plasmodium, and he also believes that 
this structure indicates closer affinities with the Acrasieae than with 
its higher relative, since the net-plasmodium, in his opinion, pre¬ 
sents conditions in the partial fusion of the individuals which are 
more nearly comparable with the conditions we have in the pseudo¬ 
plasmodium, in which the individuals are* wholly distinct. While 
it is true that the vegetative net-plasmodium may be comparable 
to a certain degree with the plasmodium of the Myxomycetes, it 
should not be regarded as the homologue of the pseudoplasmodium 
of the Acrasieae, since the latter is a phenomenon having to do with 
fructification and not with vegetation. In fact, that portion of the 
life history of the Labyrinthuleae which is in the least comparable 
with the pseudoplasmodium is not the so called vegetative net- 
plasmodium but rather the heaping up of the individuals prepara¬ 
tory to their encystment in fructifying masses. In the case of the 
dung-inhabiting Piplophrys stercorea^ for example, the external 
resemblance of the fructifying colony to that of Guttulinopsis is 
certainly striking, so that when it appeared in laboratory cultures 
