OLIVE : MONOGRAPH OF THE ACRASIEAE. 
473 
in tlie Acrasieae to discuss first the conditions existing in the simpler 
forms included in the Sappiniaceae and Guttulinaceae ; following 
which is a comparative account of the details of the development of 
the fructifications in the more highly differentiated members of the 
group embraced under the Dictyosteliaceae. 
Stalk and sorus formation in the simpler forms. — The myx- 
amoebae in the aggregations evidently seek drier places in which to 
form resting bodies; hence the pseudoplasmodia tend to turn away 
at right angles from the moist substratum. The simplest example 
of this negatively hydrotropic tendency is shown by Sappinia, in 
which, normally, isolated individuals may form simple fructifications 
by becoming stretched out from the substratum into stalked bodies 
which consist of a slender basal portion bearing an ovate or pear 
shaped cj^st (pi. 5, fig. 2). In addition to the normal, isolated, 
encysted individuals, Sappinia may also form, when growing in its 
natural environment, aggregations of more or less rounded cysts at 
the ends of small projections from the substratum. Such aggrega¬ 
tions resemble closely the sori of the more simple species of the 
Acrasieae; but they are probably formed accidentally, since, as was 
mentioned above, the amoebae fail, in my experience, to form colo¬ 
nies on a surface free from projecting particles. It is probable that 
the individuals, in responding to the negatively hydrotropic stimulus 
which directs their movements at the period of fructification, simply 
move out and away from the moist substratum as far as possible, 
and may thus accidentally form a naked mass at the end of a pro¬ 
jecting piece of straw, for example. 
Somewhat similar to these masses in general appearance, are the 
sessile fructifications of certain species of Guttulinopsis. Such 
fructifications, composed in this instance of pseudospores, form in a 
similar fashion at the ends of straws or other particles extending 
above the surface, or they may form on a surface free from projec¬ 
tions, as for instance on an agar culture tube. In this last respect, 
Guttulinopsis furnishes an important point of difference from Sap¬ 
pinia, namely, in the normal formation, by the concerted aggregation 
of many myxamoebae, of colonies of fructifying individuals (pi. 5, 
fig. 9). Guttulina protea., according to Fayod, forms somewhat 
irregular aggregations, differing from those of Guttulinopsis mainly 
in the fact that each myxamoeba becomes a definitely walled spore 
instead of a pseudospore (pi. 5, fig. 27-28). 
