92 
JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
out if enough carbonic acid be present. Or if a little lime water be 
poured in and well shaken it will become milky by the formation of 
carbonate of lime. 
In order to extract the endosperm after the embryo has escaped from 
the seed-skin the tip of the cotyledon often remains within the seed while 
the greater part may have escaped and become green, as may be seen in 
the loop-like cotyledon of a germinating Onion. In the Cocoa-nut the 
embryo, which lies in the "plug " filling the one orifice in the shell, sends 
a globular cotyledon into the cavity. This by applying itself to the inner 
surface of the endosperm dissolves and consumes it. 
If the food materials be in the cells of the cotyledons themselves, then 
these may remain below ground till all be consumed, as in acorns ; or 
they may first surrender up their starch &c., and be raised above ground 
by the radicle, turn green, and perform true leaf-functions, as in Mustard. 
In the case of Orchids, which have no endosperm and very little other 
reserve food, the germination is peculiar. 
In the first place the cells of the " suspensor," or even of the globular 
pro-embryo itself (Stanhopea) elongate and branch, burrowing into the 
placentas to extract starch, which is transmitted to the pro-embryo. It 
has been found difficult to secure the germination of Orchids, but it has 
lately been discovered that to do so with success, the seeds require the 
presence of a minute fungus in the soil, which lives a symbiotic life with 
the germinating pro-embryo, supplying the latter with proper food in some 
way not yet understood ; as occurs in the nodules on the roots of legu- 
minous plants well known to contain microbes, which fix the nitrogen of 
the air and supply that important element to the plant. To secure an 
easy germination of any Orchid, therefore, the seed should be sown in the 
same soil as that in which a plant of the species has been growing ; as 
it will have been impregnated with the particular microbe or fungus 
required by seeds of the same species of Orchid. 
The first visible sign of growth is the protrusion of the radicle, which 
instantly turns downwards to form the true root at its apex. This down- 
ward growth is called geotropism," a word which only means "a turning 
earthwards." This is presumed to be due to a sensitiveness or irritability 
of the protoplasm in the cells of the growing point, a space behind the 
immediate apex of about j\ to | of an inch ; all behind it ceases to 
elongate. If a tap-root has been laid horizontally it soon begins to bend 
downwards ; but the point of greatest curvature is higher up than the 
distance mentioned, showing that while experiments prove the irritability 
to reside in the growing part, the influence is conveyed up the root to a 
higher point, presumably by means of the continuity of the protoplasm 
from cell to cell. 
When the primary root gives rise to secondary ones these are not 
influenced by gravity so much, as they deviate at various angles from the 
main root. If, however, the growing point of the latter be cut off, then 
one or more of the lateral ones begin to grow vertically downwards. 
This has been compared with the excision of a terminal shoot of a stem, 
when one or more lateral shoots immediately grow upwards vertically to 
take its place. It is due in both cases to a redistribution of sap which 
has been checked in its due course. 
