PROCESS OF GERMINATION. P 853 
supply of oxygen is proved by the fact, that seeds will not ger- 
minate when buried too deeply in the soil, or when the soil is 
impervious to air. This explains how seeds may lie dormant at 
great depths in the soil, and only germinate when the soil is 
brought to the surface ; and hence we see the necessity of admit- 
ting air to seeds, as in the ordinary operations of agriculture. 
Process of Germination. —When the above requisites are sup- 
plied in proper proportions to suit the requirements of different 
seeds, germination takes place; but should any be wanting or 
in too great amount, the process is more or less impeded, or 
altogether arrested. The most favourable seasons for germina- 
tion are spring and summer ; and seeds sprout most readily in 
loose pulverised and properly drained soil, at a moderate depth, 
for, under such circumstances, air, moisture, and warmth have 
free access. Seeds thus placed absorb moisture, soften and 
swell, and certain chemical changes go on at the same time in 
the substance of the albumen, or, when this is absent, in the 
cells of the cotyledonary portion, by which a proper supply of 
nourishment is provided for the embryo. These chemical 
changes chiefly consist in the conversion of starch and other 
analogous substances, which are insoluble and therefore not in a 
suitable state for absorption, into soluble matters such as dextrin 
and grape sugar. The immediate cause of this transformation of 
starch is due to a nitrogenous substance called diastase, which is 
developed, during germination, from an alteration of a portion 
of the nitrogenous contents of the seed. During these chemical 
actions heat is evolved, as in the malting of Barley (see p. 856), 
and carbon dioxide given off from the combination of the 
superfluous carbon in the starchand albuminoids with the oxygen 
of the air. The nutriment being thus made available for use, it 
is absorbed dissolved in water by the embryo, which is in this 
manner nourished, increases in size, and ultimately bursts 
through the integuments of the seed. Its lower extremity or 
radicle (fig. 16,7), or one or more branches from it (fig. 765, r), 
is commonly protruded first from its proximity to the micropyle, 
which is the weakest point in the integuments, and by taking a 
direction downwards becomes fixed in the soil, whilst soon after 
the opposite extremity elongates upwards (fig. 16, t), and is 
terminated above by the plumule, which is the first terminal bud 
or growing apex of thestem. At the same time the cotyledonary 
portion is either left under ground or is carried upwards to the 
surface. The embryo during this development continues to be 
nourished from the matters contained either in the albumen or 
cotyledonary portion, and ultimately by continuing to absorb 
nutriment it is enabled to develop its first leaves (primordial) 
( fig. 18, d, d,) and root, 7. The young plant is now placed in a 
position to acquire the necessary nourishment for its further 
support and growth from the media by which it is surrounded, 
and is thereby rendered independent of the other parts of the 
