20
Scientific Memoirs by
Plate II, fig. 5). In those cases in which the growth is vigorous the resulting
mass becomes of very considerable thickness, and of a bright pink tint, ranging
from strong salmon-color to pale rose-madder. The color from the very outset
is pink, but is at first relatively pale and deepens gradually as time goes on.
The texture is at first soft but firm, and in some cases retains these characters
throughout. In others, however, after a time softening takes place internally,
and, the change being accompanied by processes of gaseous evolution, large
bubbles come to protrude on the surface. In very old cultivations, even on
what appear to be quite normal potatoes, a thin peripheral fringe sometimes
makes its appearance around the margins, but in all other cases these are pro-,
minent and sharply defined. Such fringes, when present, are ordinarily almost
colorless, or very pale pink or buff. This alteration in color and habit are apparent-
ly due to changes in the re-action of the medium, as in cases where potatoes of
manifestly abnormal acidity are employed the growth throughout remains rela-
tively thin and almost colorless. The influence of the re-action of the agent as
the cause of the alteration in color is also indicated by the fact that acids, even
dilute acetic acid among the number, rapidly remove the color even . from deeply
tinted normal growths.
In most instances, as is the case with similar growths in the species pre-
viously described, with the exception of species 8, it is not easy successfully to.
transfer the growth from one potato to another even when in the primary one
it would appear to have been fairly established. In one case, however, complete
acclimatisation would appear to have occurred, and a continuous series of transfers
has in it been carried on from the end of June 1890 until the present time, and,
although the growth has not been so vigorous, since the cold season set in as it
was during the summer and autumn, in no instance have they proved unsuccessful.
In the course of this prolonged series of cultivations phenomena have manifested
themselves, which, although not indicative of such profound alteration in habit
and properties as those which have been described as occurring in a correspond-
ing series of cultivations of species /3, very clearly show the presence of a strong
tendency to the establishment of temporary varieties. The materials derived
from potato cultivations have invariably grown readily when transferred to ordin-
ary nutritive Agar-agar, and in many cases have at once resumed the properties
and habit of the normal growth in that medium. In other cases, however, the
growth was at first completely confined to the surface of the medium, , the power
of intersticial, anaerobic growth being only gradually regained in the course of
repeated, transfers from one Agar-agar medium to another, and in' still other cases
a persistent aerobic habit was retained throughout prolonged series of transfers
to Agar-agar and nutritive broth. Some potato , cultivations have throughout
shown a retention of capacity for anaerobic growth in Agar-agar ; others have
apparently lost it entirely during the whole period in which they were kept under
observation and a large number, whilst apparently devoid of the property at