478 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
undifferentiated myxamoebae ; and with haematoxylin, which colors 
the cellulose walls of the stalk dark blue, the membrane becomes 
but little stained. Further conclusive evidence that the membrane 
is mucus rather than cellulose, is furnished by the fact that it stains 
instantly with muchaematin. 
Chloriodide of zinc applied to the developing fructification dis¬ 
closes the fact that cellulose is being deposited around the proto¬ 
plasm of each stalk cell, even in a very young stage of vacuolation. 
A plasmolyzing agent such as a salt solution also shows clearly the 
limits of cellulose deposition; by this means water is extracted 
from the vacuolated cells, thus causing those which have no firm 
membrane of cellulose to lose their vacuoles entirely and to lie loose¬ 
ly as shrunken cells in the mucous sheath. Those, however, in which 
cellulose formation has begun, remain cemented together and the 
more or less rigid w^alls preserve somewhat the vacuolated structure. 
It is, furthermore, a rather curious fact that while young stalk cells 
respond to the cellulose test at once, the stalks and spores of mature 
fructifications require from three days to a week to show the char¬ 
acteristic blue color, a fact which may perhaps be attributed to the 
resistance offered by the mucous covering which encloses them. 
The interesting question as to the nature of the substance in the 
vacuoles of the myxamoebae of the stalk is one involving many 
difficulties. Many microchemical tests with litmus and methyl 
orange solutions, as recommended by Pfeffer, have given unsatis¬ 
factory results as to the acid or alkaline reaction of the vacuolar 
fiuid. On the supposition that the dissolved substance of the 
vacuoles might be uric acid, as is said to be the case in the con¬ 
tractile vacuole of the amoeba and other protozoon forms, 
(Griffiths, ’89), the murexide test was repeatedly tried, but the 
resultant color reactions were unsatisfactory. 
The fructifying pseudoplasmodia of the various members of the 
Dictyosteliaceae are thus seen to be made up of two kinds of indi¬ 
viduals : the normal myx:amoebae, each of which • is ultimately to 
become a spore in the sorus at the summit, and the differentiated 
individuals, which together form the supporting stalk. The pseudo¬ 
plasmodia of the more complicated members of the Guttulinaceae 
likewise form fructifications which show a slight degree of differ¬ 
entiation, in that some of the myxamoebae become rounded or oval 
spores or pseudospores of the head portion and others in the stalk 
