ANDREWS: PROTOPLASMIC STREAMING IN Mucor 497 
and shape, due mostly to the streaming back and forth. This 
caused some of the vacuoles to be separated into several or some- 
times many smaller ones and in other cases caused small ones 
to fuse into one or more vacuoles. 
The division of vacuoles, especially the larger ones, was well 
shown in those instances where a stream of protoplasm (FIG. 9) 
divided on coming to a branch. Then, frequently about one half 
or often only a small part would go into the branch. Whether 
the streaming is slow or fast the vacuoles are always carried along 
with the whole mass. They are convex on the end toward which 
the flow is directed and concave on the opposite end. This shows 
that a relief of pressure exists in the direction of streaming. Some- 
times the streaming stops very suddenly with a jerk and when 
starting frequently does so in the same way, although the factors 
producing streaming are active. This kind of sudden cessation of 
motion generally lasts for from one to a few seconds, when stream- 
ing is resumed at the normal rate. It is caused, as careful observa- 
tion will show, by a mass of temporarily impermeable protoplasm 
suddenly entirely plugging up the cavity of the filament at some 
point. As soon, however, as more water is removed, as for example 
by osmosis, transpiration, or some other factor, the pressure is 
gradually relieved and the obstruction suddenly gives way, allow- 
ing a recommencement of streaming so suddenly as to cause the 
protoplasm to appear as if jerked forward. Unless the obstruction 
is removed the filament beyond that point frequently collapses, 
due to excessive transpiration or other factor. Sometimes the 
velocity would vary for no apparent reason, as is known to be 
the case in other plants. 
At times when no streaming was visible an extremely thin 
layer of protoplasm between the large vacuoles and the ectoplasm 
could be seen to be in motion. Part of the time it moved in the 
Same direction as the streaming had moved and sometimes in the 
reverse direction. I was unable to see it moving in the opposite 
direction to the streaming protoplasm. I can therefore not agree 
With Schréter* on this point but find, as stated by Ternetz for 
Ascophanus carneus, that during streaming all of the moving proto- 
plasm of Mucor stolonifer and M. Mucedo goes only in one direction. 
* Schréter, loc. cit. 30. 
