OLIVE: MONOGKAPH OF THE ACRASIEAE. 
479 
portion retain their elongated shape; whereas the simpler species 
show no differentiation whatever in their fructifications. 
The resultant fructifications of the Dictyosteliaceae^ as indicated 
above, present various habits in the four genera composing the 
group. They all agree, however, in the fact that the basal cells of 
the fructifications are generally greater in number or are broader 
than the other stalk cells, thus forming an expanded foot. Further¬ 
more, all show more or less variation in appearance under different 
conditions. For example, in most cases, the breadth of the stalk 
accommodates itself to the size of the pseudoplasmodium; the larger 
the number of myxamoebae in the latter, usually the broader and 
firmer the support. In a large fructification, for instance, there may 
be as many as ten or more polygonal stalk cells in optical cross sec¬ 
tion near the base, and only one at the distal portion, fewer and 
fewer cells being thus differentiated the higher it rises above the 
substratum. Weaker fruit bodies, on the other hand, may have but 
one row from the beginning; and, according to van Tieghem, Acra- 
sis granidata and Dictyosteliiim lactemn^ under normal conditions, 
possess only one row of stalk cells throughout the entire length of 
the fructification. 
Branching fructifications in the Bictyosteliaceae. — Polysphon- 
dylium is the only representative of the Bictyosteliaceae that pos¬ 
sesses fructifications which are normally branched, while those of 
the other three members of the group, on the other hand, are 
usually simple. Under certain conditions, however, the fructifica¬ 
tions of Dictyosteliiim and Coenonia may each bear one or more 
small branches, disposed along the main axis. Furthermore, Poly- 
sphondylium may also show an occasional unbranched fructification, 
which consists of a stalk bearing a single sorus of spores at the top, 
and which appears similar in all respects to an unbranched fructifi¬ 
cation of Dictyostelium (pi. 8, fig. 118, a). Such a phenomenon 
points clearly to the near relationship of these two genera, and 
indicates, as do the variable, simple, or branched fructifications of 
Dictyostelium and Coenonia, that the stalk should in reality have 
little weight in this group as a character of generic value. 
Van Tieghem has noted the fact, in the case of Coenonia, that 
whereas the fructifications are normally simple in cover glass cul¬ 
tivations, a luxuriant culture yields frequently a fructification in 
which the principal stalk bears a verticel of three equidistant 
