OLIVE : MONOGRAPH OF THE ACRASIEAE. 
491 
strongly heliotropic. Finally, the stalks of certain species of the 
Dictyosteliaceae show when young a spiral twist, the cause of which 
is as yet undetermined. 
Systematic Relatioj^s of the Acrasieae. 
Affinities. — De Bary (’ 87 ) and other writers on the Mycetozoa 
evidently believed in the common origin and close relationship of 
the Acrasieae and the Myxomycetes, as well as in the development 
of the one from the other. De Bary regarded it as more probable 
that the plasmodium of the Myxomycetes has proceeded directly 
from the pseudoplasmodium of the more simple Acrasieae rather 
than that the converse order of development was followed. He 
suggests (p. 443) that “forms like Guttulina may have developed 
phylogenetically in two divergent directions, on the one hand into 
the more highly differentiated Acrasieae, on the other into forms 
which produce plasmodia.” 
Harper (: 00, p. 235) is of the opinion that “there can be no 
question that the Acrasieae represent simpler forms out of which 
the Myxomycetes have developed, and we thus have a develop¬ 
mental series leading from simpler to more complex forms.” He 
adds, however, that “the plasmodium and capillitium, occurring 
only in the more specialized members of the group, are plainly 
secondarily acquired structures developed as additions to the struc¬ 
tural features of the Acrasieae and are not to be directly homolo- 
gized with 23hysiologically equivalent structures in other groups.” 
De Bary and others, on the other hand, would even derive the 
plasmodium from the pseudoplasmodium and conceive that the 
aggregation of individuals of the loAver groiqi becomes fused into 
one mass of protoplasm and that the mass then prolongs its vegeta¬ 
tive existence for an indefinite time before proceeding to fructify. 
In other words, the coalescence of the myxamoebae in the Myxomy¬ 
cetes into a plasmodium and the final redivision of the jdasmodium 
into individuals would take the place of the simple aggregation of 
individuals in the Acrasieae. 
There can be no question as to the common origin of the Myxomy¬ 
cetes and the Acrasieae. When, however, the two groiq^s are care¬ 
fully compared in all their structural and j^hysiological phenomena. 
