OLIVE: MONOGRAPH OF THE ACRASIEAE. 
477 
lated myxamoebae on the summit of the stalk column, which are 
surrounded and surmounted by a thin film of undifferentiated 
individuals on their periphery. This peculiar differentiation thus 
goes on rapidly at the summit of the aggregation, so that there is 
constantly being formed a firm support up which the colony climbs 
(pi. 8, fig. 110). 
As the mass external to the stalk moves slowly upward, the 
ascending cells secrete a mucous substance which is deposited on the 
central axis, so that the latter becomes bounded by a sharply defined 
mucous sheath, and, as the colony ascends higher still, the secretion 
left behind by the whole mass covers the stalk below, thus adding 
considerably to the strength and rigidity of the support (pi. 7, figs. 
97, 106). At the bottom of the stalk also, mucus is especially 
abundant and serves to bind the base firmly to the substratum (pi. 
6, fig. 88). Brefeld mentions an interesting phenomenon which 
occurs when bacteria interfere with the normal development of 
Polysphondyliiim violaceiim. Under such conditions, the stalk may 
not be attached to the substratum, but may remain free in the 
pseudoplasm odium. In all probability, such an abnormality is pro¬ 
duced by the activity of motile bacteria, which by their movements, 
break loose the delicate mucous membrane from the substratum. 
Normally, however, the attachment is comparatively firm, although 
in transferring spores with a platinum needle, the whole fructifica¬ 
tion may rather easily be torn away from the substratum, especially 
after a sidewise push to the stalk has disrupted the mucous mem¬ 
brane at the base. Where the stalk is curved, this external mem¬ 
brane, which is usually difficult to detect, may be readily seen, 
stretching across the sinus (pi. 7, fig. 97). Imbedded in it may 
sometimes be observed isolated, vacuolated cells, whose walls show 
cellulose reaction, and which have evidently failed to join the other 
members of the column before becoming differentiated (pi. 8, fig. 
111 ). 
This membranous covering which encloses the stalk was said by 
Brefeld to be cellulose. It is true that it turns a faint blue with 
chloriodide of zinc, but it does so only after some hours’ exposure to 
the reagent, while, on the other hand, the cellulose walls of the 
young stalk cells show the blue reaction at once. At first, on 
being placed in a drop of chloriodide of zinc, the enclosing 
membrane turns yellow, just as does the surrounding colony of 
