28 i 
Protoplasm by Aid of Microdissection. 
The membranes so far discussed have been those on ‘ naked ’ masses of 
protoplasm, such as myxomycetes and Amoebae and escaped protoplasm. 
It has long been believed that protoplasm within a cellulose wall is bounded 
by a membrane which by Pfeffer and others has been looked upon as 
the osmotically functioning region of the plant cell. 
This outer protoplasmic layer next to the cellulose wall de Vries 
termed the ectoplast. Direct evidence of its presence in the living condition 
is very difficult to obtain. I have, however, observed it after degeneration 
and consequent coagulation have made it coherent and rigid enough to 
be separated from the protoplasm. 
The hyphae of the bread-mould Rhizopus are frequently very turgid. 
Occasionally a filament can be found in which the protoplasm is a firm jelly 
and is sufficiently turgid to cause a slight protrusion of the protoplasm from 
the hypha when this is ruptured. By pressure with a needle some dis- 
tance behind the torn end, the rod of protoplasm can be made to ooze 
out like oil paint from an artist’s tube. This protoplasmic jelly is suffi- 
ciently rigid to hold its shape until dissected. It remains immiscible in the 
watery medium. Dissection will sometimes reveal, next to the protoplasmic 
rod, a delicate membrane which on further dissection proves to be a thin 
outer layer of highly viscous, gelled protoplasm enveloping the rod, 
and far more rigid and resistant than the soft protoplasmic jelly within. 
This thin membrane may be partially freed from the rod of protoplasm. 
I know of no other satisfactory designation of this firm outer layer than 
that it is the ectoplast, the plasma-membrane (in a degenerate, gelated 
state). 
The Vacuolar Membrane. I have referred to the difference in be- 
haviour of freed protoplasm from pollen tubes. Frequently, the protoplasm 
mixes with the surrounding water immediately on escaping. If the larger 
vacuoles thus set free by the escaping protoplasm of a germinating pollen 
grain are observed, they will be seen to be surrounded by a thin but plainly 
visible protoplasmic membrane. Clinging granules can be seen to glide 
along its surface. This membrane permits the vacuole to maintain its 
identity for several seconds while free in water. The volume of the vacuole 
slowly increases, due to osmosis, until it becomes twice its original size, when 
it bursts. 
The vacuolar membrane may, when exposed to water, undergo a 
decided change. The many small vacuoles ejected with the liquid proto- 
plasm from a hypha of the bread-mould Rhizopus are found, when exposed 
to water, to possess a quite resistant membrane which tolerates considerable 
pressure. But when these vacuoles are handled while still within the mass 
of protoplasm they burst at the slightest touch. 
This view of the vacuolar membrane as a somewhat differentiated layer 
of protoplasm closely comparable with the external plasma-membrane 
