PHYSARELLA MIRABILIS PECK AND STEMONITIS FUSCA ROTH 283 
membrane surrounding these capillitial primordia, wall substances 
are next secreted. I am as yet unable to state positively whether 
the thin wall deposited early in capillitium formation is folded or 
actually pushed inward by subsequent external deposits from the 
surrounding plasma membrane ; or whether the tubular cavity gradu- 
ally increases in size, deposition thus resulting in a constantly increased 
total diameter of the capillitial threads. I am inclined to think that 
the former process obtains to a certain extent and that actual diminu- 
tion in size of the lumen of the capillary tubules sometimes conse- 
quently results. The substance secreted to form the walls of these 
hollow threads is presumably plastic for some little time after forma- 
tion. Furthermore, there may undoubtedly occur a wrinkling or 
folding of the thread during the process of drying, particularly in 
regions where it is comparatively broad. This latter appearance is 
more frequent in Stemonitis fusca. However, in any case, as has been 
previously stated, there can very frequently be observed within the 
thread a lumen of greater or lesser diameter. I know of no good 
reason why practical solidity should not occur in certain cases; such, 
for example, as would result from a deposit in a tubular space of ex- 
tremely capillary proportions. 
It is further shown beyond doubt in the case of Physarella the 
same method of deposit obtains in the formation of walls about both 
Hme knots and capillitial threads, as that seen in the formation of the 
inner part at least of the sporangial wall. The first few figures show 
clearly the continuity of the boundary of those parts. Although the 
external surface of the outer peridium appears thicker, presumably 
from hardening through exposure to the air, I have no doubt but 
that the whole sporangial wall is of similar character and deposited by 
protoplasmic secretion. 
The large amount of lime in the mature sporangium of Physarella 
suggests an approach to the condition obtaining in Fuligo varians in 
regard to the amount of lime present. The old analysis of Reinke 
and Rodewald ('8i) credits that species of Fuligo with 27.7 per cent 
of calcium carbonate, and 5.33 per cent of calcium in combination 
with higher fatty acids. The absorption, deposition, etc., of this 
calcium carbonate in these Myxomycetes furnishes an interesting 
problem, since, as is well known, CaCOs is soluble only in 100,000 
times its own weight of pure water. It is further curious that some 
species should provide themselves with such large quantities of 
calcium carbonate, while others apparently lack it entirely. 
