ill!Ill

4. Lastly
HISTORY OF DIATOMS. 23
the Rev. Wm. Smith has described a fourth method of re-
Fig. 16.
Fig. 16 Reproduction of I'an Heurckia rhomboides
Brcb.
A. Two mother cells fusing their protoplasmic
contents in order to form two sporanges.
production, in which a single frustule
gives birth to two sporanges. This
has been recorded in
phenomenon
Achnanthes and Rhabdonema, but
as it has never been since observed
it is thought that it must have been
an error in observation on the part of
the illustrious English diatomist.
To sum up it seems probable that
diatoms most frequently return to
the sporangial form by an act of
rejuvenescence without actual repro-
duction, but that when it really does
take place it is produced by the
union of two frustules, which give
birth sometimes to a single sporange,
but generally to two sporanges.
We shall here draw attention to a
very remarkable idea ventilated by
Dr. Ad. Schmidt. "I observed,"
said he, "in 187 1 the regeneration
of Gomphonema mustella Ehr in
thousands of cases, and what I have
just said has not been invalidated B. Two auxospores larger than the four
empty valves, between which they are formed,
arrived at their complete development and at the
point where the terminal hoods detach them-
by
selves to enable the sporangial frustules to pass.
a single exception. When these
C. Sporangial frustules arrived at their complete
development and still covered with the Gomphonema reproduce they have
hoods which they have drawn along on leaving ... .
the auxospores.
. ....
their stipes, and unite with their
venters turned towards each other, but in an inverted position, that is
to say, so that the anterior apex of one frustule rests against the
posterior apex of the other."
"
This fact," he concluded, " in my opinion
disposes of the vegetable nature of diatoms." (! ?)
In concluding this section it may be noticed that, according to Kitton (')
2
and Professor Samuel Lockwood, ( ) diatoms may possess microspores so
small that they can pass through filter papers. Lockwood appears to
(') Kitton: On the Mysterious Appearance of a Diatom, J.Q.M.C, Ser. II., Vol. II. (1885),
pp. 178-9; 206. J.R.M.S (1885), p. 1,041.
(
- ) Lockwood, Prof. Samuel : Raising Diatoms in the Laboratory. Journal New York Mic.
Soc. (1886) II., p. 153, two plates; J.R.M.S. (1887), p. 626.