The chain of connected processes and
transformations which extends from the quiescent seed
to the actively developing juvenile plant may be regarded,
in general, as the phenomenon of germination.
The first and most important of these changes, and
the one upon which all the others depend, is the
absorption of water. A study of this prerequisite
for success in germination therefore seems fundamental
to the elucidation of the entire process, more
especially as the question of successful germination
bears so definitely on many problems of practical
agriculture, as well as on aspects of more purely
academic interest.
Relevant to this main problem is the question
of how substances dissolved or suspended in the water
supplied to the seed affect this process. Here again,
as in the main problem, points of academic interest
arise, but these are overshadowed by more practical
questions because of the increasing use of chemical
dressings as preventives against the attacks of seed -
borne and soil fungi. Another aspect of the problem
is the mode of penetration of these added substances
into the seed, where some fungus may be located,
which the fungicide must reach if it is to accomplish
its beneficial work.
This present thesis, therefore, is a report
of studies on the intake of water by the seed, and
the penetration of various substances dissolved in the
water supplied to the seed and their effect on
germination. It must be made clear that the work is,
in the main, exploratory in nature for when initiated
the whole conception of the initial stages of water
intake by the seed had been recast by the researches
of Nelson and MacSween on the Broad Bean, Vicia Faba
L., published in 1933. Until that time the path of
water intake had been defined as taking place through
the micropyle, and the general surface of the seed had
been regarded as of minor importance in so far as it
affected the intake of water. That this conception is
not true, at least for the earlier phases (the first
six hours approximately), has been proved. The newer
conception is that the first stage is the hydration of
the testa, which, being of a colloidal nature, absorbs
water by imbibition. The hydrated testa is known to
be an imperfectly semi-permeable membrane, and it has
been suggested that further water intake is by osmosis
through this structure. Some doubt still exists as to
the exact nature of the substance which acts as the
"attractor" of the water through the seed-coat, but,
in the main, the steps in the process as outlined by
Nelson and MacSween hold good. A subsidiary point of
considerable importance brought out by these workers
is that each seed must be regarded as an individual,
because when using genetically standardised material
it was shown that while the curve of water intake by
a seed of Broad Bean had characteristics similar to
another seed, yet they differed in their relation to
time. These differences may be, and probably are,
related to the pre-history of the seed, e.g.
maturation, storage, etc. (Hysteresis of the seed-coat
colloids probably covers much of this).
