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Scientific Memoirs by
and absolutely distinct from those of either δ or λ (Plate IV, Fig. 8, a). Many at-
tempts at inoculation prove abortive, but at intervals of months ever since it was ori-
ginally obtained two years and-a-half ago the tube-cultures have yielded growths on
potatoes of uniform and perfectly distinctive characters, showing not the slightest
evidence of any tendency to assume those proper to the healthy growth of any other
form. Again, in the case of form y, which has throughout been very insusceptible
of culture on potatoes, really successful growths have only been obtained twice—
once in the beginning of 189o, and for a second time after an interval of two years,
but in spite of this prolonged interval during which the organism had been subjected
to continuous cultivation in agar-agar media, the second growth presented the
same essential features as the first one, and showed no evidence of any tendency to
assume those proper to healthy growths of any other form. In the case of form μ
also only two successful cultures on potatoes have hitherto been obtained. The
first of these was on a tuber inoculated on the loth of November 1891, and the
second on one inoculated on the 21st of June 18 93. The source from which inocu-
lation was effected was, in the first case, one of the very earliest, and, in the second,
the latest of the continuous series of tube-cultures in agar-agar proper to the form.
But in spite of this and of the fact that numerous unsuccessful attempts at cul-
ture had been carried out during the intervening period, the second growth exactly
reproduced all the essential characters of the first one. In both cases alike
the growth was of a strong Indian yellow colour, comparatively thin, very con-
spicuously nodulated as though composed of confluent colonies, and consisting of
relatively short, thick commas (Plate IV, Fig. 10, b). Cases like these afford speci-
ally strong evidence of the presence of essential, specific peculiarities between the
organisms furnishing the different growths, for in them there can be no suspicion
that the habit of growth is dependent on any peculiarity in the original substratum
productive of variation in the organism of such persistent nature as to influence
the character of subsequent growths directly derived from the primarily modified
one. Where the growths in a continuous series of potato-cultures uniformly
present certain distinctive features, it is possible to regard the phenomenon
as the result of peculiar and persistent effects arising from peculiarities in the
primary tuber ; but when we find isolated growths, occurring at wide intervals
and in no way directly related to one another, reproducing distinctive peculiar-
ities, this is no longer the case, and we must regard the differences in the growths
as indicating intrinsic differences in the nature of the organisms producing
them. It is unfortunate that so few forms should persistently retain a capacity
for healthy growth on potatoes, but the significance of the fact that in those
cases where the capacity is retained there is a total absence of any assimilation
in the characters of the resultant growths after the most prolonged exposure of
the formative organisms to the influence of like external conditions is not
affected because other forms, which originally yielded vigorous and characteristic
growths, have new either entirely lost all power for growing under the con-