ill!Ill

52
CULTIVATION OF DIATOMS.
The purity of the products employed in the solution is, according
to Mr. Gill, essential. If one wishes to succeed, too much care cannot
be taken to ensure the absence of every trace of arsenic, mercury or
silver. The presence of arsenic which is so often found in ferric chloride,
in consequence of its being frequently manufactured with impure hydro-
chloric acid, is one of the commonest causes of failure.
As Dr. Miquel also points out, Mr. Gill discovered that the direct
rays of sunlight are absolutely harmful to the greater part of the cultivation.
He exposed his flasks to the direct sunlight on a board close to some
glass windows which were situated N.N.W.,
at the same time inter-
posing between the glass and the flasks a plate of pale green glass
of the
height of the flask and a wooden board slightly higher than the liquid.
All the cultivations had been planted with one or more frustules,
transferred with a capillary tube. "This," said he, "is the simplest
and quickest method and also ensures absolute certainty
that there is
no other diatom in the final drop which is to be used for the purpose
of planting the flask.
The experiments of Mr. Gill were tried on a sufficiently large number
of forms, among which we may mention PL Angulatum, Cymatopkura
solea and Ellipiica, various Nitzschia, Cymbella and Navicula. All these
forms were made the subject of numerous successive cultivations, and he
had about ioo in his possession at the time of his decease. Some of
these cultivations are unfortunately dead, perhaps from want of assimilable
matter or for other unknown causes ; but a considerable number of them
are still
living. All of these, with voluminous notes by Mr. Gill, are
in my possession. I hope to be able to follow these cultivations
through a number of generations, and if the opportunity
to publish the results obtained from them.
E. Results of Experiments with Cultivations.
occur I intend
Dr. Miquel has published in " Le Diatomiste " the technical methods of
treating cultivations, and his experimental researches in the physiology, mor-
phology, and the teratology of diatoms, which have resulted from the beforementioned
cultivations, have been published in the " Annales de Micrographie."
We shall in a few words summarise the results obtained by the
learned observer, but we refer the reader who desires a detailed account
to the above-mentioned publication in which the experiments are fully and
minutely described.
i. Effect of Temperature. A. Damp
temperature between 15 and 30 C.
heat. Diatoms flourish at a