on, growth, etc.

Let us take one of the simplest cases--an alteration in form. A
cylindrical cell of the alga Stigeoclonium assumes, as Livingstone
(Livingstone, "On the nature of the stimulus which causes the change
of form, etc." "Botanical Gazette", XXX. 1900; also XXXII. 1901.) has
shown, a spherical form when the osmotic pressure of the culture fluid
is increased; or a spore of Mucor, which, in a sugar solution grows
into a branched filament, in the presence of a small quantity of acid
(hydrogen ions) becomes a comparatively large sphere. (Ritter, "Ueber
Kugelhefe, etc." "Ber. bot. Gesell." Berlin, XXV. page 255, 1907.)
In both cases there has undoubtedly been an alteration in the osmotic
pressure of the cell-sap, but this does not suffice to explain the
alteration in form, since the unknown alterations, which are induced in
the protoplasm, must in their turn influence the cell-membrane. In
the case of the very much more complex alterations in form, such as we
encounter in the course of development of plants, there do not appear
to be any clues which lead us to a deeper insight into the phenomena.
Nevertheless we continue the attempt, seeking with the help of any
available hypothesis for points of attack, which may enable us to
acquire a more complete mastery of physiological methods. To quote a
single example; I may put the question, what internal changes produce a
transition from vegetative growth to sexual reproduction?

The facts, which are as clearly established from the lower as for the
higher plants, teach us that quantitative alteration in the environment
produces such a transition. This suggests the conclusion that
quantitative internal changes in the cells, and with them disturbances
in the degree of concentration, are induced, through which the chemical
reactions are led in the direction of sexual reproduction. An increase
in the production of organic substances in the presence of light,
chiefly of the carbohydrates, with a simultaneous decrease in the amount
of inorganic salts and water, are the cause of the disturbance and
at the same time of the alteration in the direction of development.
Possibly indeed mineral salts as such are not in question, but only in
the form of other organic combinations, particularly proteid material,
so that we are concerned with an alteration in the relation of the
carbohydrates and proteids. The difficulties of such researches are very
great because the methods are not