474 PKOCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
In those fructifications of Giittulinopsis and Guttulina in which 
the sori are borne on stalks, certain myxamoebae usually become 
more or less differentiated in form and function, so that slightly 
altered individuals become stalk cells of the supporting structure, 
while others form a spherical sorus of spores or pseudospores at the 
summit. In the fructifications of Guttulina rosea^ and of some of 
the short stalked species of Guttulinopsis, for example, the cells of 
the head become in the first instance spherical spores, or in the sec¬ 
ond, pseudospores, while those of the stalk or foot portion in both 
cases retain the elongated or wedge shaped form of the myxamoebae. 
In that form of the Guttulinaceae which we may regard as having 
the simplest structure, Guttulinopsis vulgaris^ we may meet with 
sessile as well as stalked sori in the same culture; such a phenomenon 
evidently detracts much from the value of the stalk as a specific 
character, whereas the culmination of differentiation in this group 
is reached in the long stalked Guttulinopsis clavata^ in which 
elongated stalk cells are firmly cemented together by an abundant 
enclosing mucus. When such a fructification is placed in water, 
the base remains intact, while the pseudospores of the head deli¬ 
quesce, so that where the top of the stalk is broken off, the adherent 
cells projecting from the apex give the appearance of a conical 
columella (pi. 5, fig. 21). The fructification of the interesting form, 
Guttulinopsis stipitata^ although it may have even a longer stalk 
than that of Guttulinopsis claoata, sometimes reaching the height 
of more than a millimeter, furnishes an exception in that it shows 
no differentiation whatever in the shape of the stalk and head cells, 
these being alike irregularly spherical throughout the whole fructifi¬ 
cation. 
As stated above, the individuals of the sori of Guttulinopsis, 
during the period of rest, lose water and shrink somewhat as the 
fructification dries, and finally become encysted, forming without 
exception, pseudospores which are unprotected by a cell wall of 
any kind. Guttulinopsis is, in my experience, rarely met with in 
the winter months, while representatives of the spore-bearing spe¬ 
cies may, on the other hand, be met with throughout the year. It 
is possible that the absence of a cell wall in the case of the pseudo¬ 
spores of Guttulinopsis may account for this fact. 
Stalk for 7nati on m the Dictijosteliaceae. — The differentiation in 
the simpler groups of Guttulinaceae is indeed slight when compared. 
