Protoplasm in Coenocytic Hyphae . 503 
ment will therefore be noticeably greater along the axis of 
the tube where there is least friction. For this reason every 
transverse surface tends to become more and more convex 
in the direction of the movement, which accounts for the 
heightened convexity of the forward end of the vacuoles 
and the flattening or introversion of the rear end. 
There is, furthermore, less resistance to axial movement 
just in proportion to the thinness of the transverse layers of 
protoplasm ; therefore a thin-walled vacuole will tend to move 
faster than a thick-walled one ; and this action, coupled with 
the tendency of the transverse layers to become thinner as 
movement progresses, dependent upon density, viscosity, elas- 
ticity and other factors, brings about the frothy appearance 
in the rear of a long vacuole. 
It is evident that if the movement is due to the change in 
water-content at the extremities, streaming toward the free 
aerial parts should be more frequently seen than the opposite 
movement ; and this is the case, the observation cited in detail 
being almost typical. It would also follow that streaming 
would be more constant toward and into growing branches 
and developing sporangia than toward other parts, for at 
these places both metabolism and extension of the walls are 
demanding material and removing resistance from the advanc- 
ing column. This also agrees with observation, and in fact 
is the particular case noticed by De Vries, mentioned at the 
outset. The same greater proportion of movement toward 
advancing extremities and into sporangia has been observed 
by De Bary 1 in the streaming of the Myxogastres. 
The number of conditions which may have an influence 
upon the movement is considerable, and their interaction very 
complex. But foremost among them, after sufficient turgidity 
is attained, is undoubtedly the facility of absorbing water in 
one part and its release in a distant part. Some attention 
was given to cases where this was minimized, and a specific 
instance or two may be cited. A culture of Macor racemosus , 
Morph, and Biol, of Fungi and Myc., 426. 
