The Retention of Vitality of Moss Protoneiria. 141 
dried nearly fifty years ago, and which has remained dormant ever 
since. The cells of the filament possess all the characters of true 
resting cells ; they have become very much enlarged, and an intense 
thickening of the walls has produced considerable distortion, not 
only in the shape of individual cells but also in the growth of the 
whole filament (Fig. 2). In some cases a number of dwarf branches 
have been produced, which by being crowded closely together have 
given the filament the appearance shown at a in this figure. 
The walls of the cells are extremely thick and lamellose and 
have assumed a deep brown colour. The thickenings are somewhat 
irregular, often with the production of projections both on the inside 
and on the outside of the wall; the ends of the cells are frequently 
enlarged to form a head with densely striated walls (Fig, 3, B). 
Circular markings can also be seen on the lateral walls of some of 
the cells showing where side branches have become detached from 
the main filament (Fig. 2, A, b). 
Two kinds of cells can be distinguished from one another by 
their contents. The great majority have the structure shown in 
Fig. 3, B, where the walls are enormously thickened and a lining 
layer of cytoplasm can easily be detected under the microscope by 
reason of a number of minute globules of oil which it contains. In 
these cells a nucleus lying close to the cell-wall can frequently be 
seen without staining. A few other cells are rendered most con¬ 
spicuous by being completely filled with large globules of a greenish- 
yellow oil, which gradually turns to a deep brown colour, and finally 
black, on treatment with a 1% solution of osmic acid. The walls 
of these cells are often somewhat less thickened than those of the 
first kind (Fig. 3, A). 
In ordinary green protonema-filaments reserve food is stored 
in the form of starch ; the existence of a fatty oil in the cells of the 
resting filaments is unique, and is interesting as being correlated 
with their extreme retention of vitality. 
When suitable conditions for growth are supplied, young 
filaments are produced as outgrowths from the walls of the resting 
cells, and the latter gradually lose their oily contents. At first the 
young filaments are colourless, but as cross-walls are formed and 
the filament increases in length small scattered disc-shaped chloro- 
plasts appear. The cell arising directly from the resting filament 
is slightly swollen at the base (Fig. 2, B, c ) and appears in all cases 
to remain permanently colourless, and its wall gradually assumes a 
light brown colour (Fig. 1, C, a). It is not until three or four cross¬ 
walls have been produced in the young filament that the cells 
