HYBRIDISING AND RAISING SEEDLING ORCHIDS
A new interest has been added to Orchid culture by the pursuit of
hybridising and raising seedling Orchids, which commenced with _Calanthe
Dominyi_, raised in the nurseries of Messrs. Veitch and recorded in the
_Gardeners' Chronicle_ in 1858. The practice has now become general, and
a large number of Orchidists arrange for the production of new Orchids
from seeds, while even in small collections some attention is given to
the matter. When the engrossing pursuit is first taken up, the operator
should neglect no opportunity to make himself conversant with the
structure of the flowers. This may be done effectually by carefully
examining any available flowers, and by making longitudinal sections of
the bloom by cutting them in two, commencing at the apex of the column
and finishing at the ovary and pedicel. This operation exposes the
various organs that are concerned in the fertilisation of the flower.
In most Orchids, such for instance as Laelias and Cattleyas, it will be
seen that the pollen masses are situated at the apex of the column
covered by the anther cap, the stigma being in a cavity in the face of
the column beneath it.
In Cypripedium there are two developed anthers; the viscous pollen
masses are not enclosed in cases, but are placed opposite each other;
the stigma is a shield-shaped body seen inside the lip on the under
side of the column, and the stigmatic surface is not viscous.
The details of the structure of the flowers being fully understood, it
will readily be seen that the first process in the production of seeds
is to fertilise the flower intended to bear the seed capsule with the
pollen of the other parent selected. This is readily accomplished by
lifting the pollen masses beneath the anther-cap with a thin pencil or
sharpened stick and placing them on the stigmatic surface of the
seed-bearing parent.
Flowers which are intended to be fertilised for seed-bearing should have
their own pollen carefully removed before the pollen taken from the
other plant is introduced, the pollen removed being used to effect the
reverse cross, or to fertilise another species if desired.
In fertilising small flowers with the pollen of larger species, as in
the case of _Sophronitis grandiflora_ with the pollinia of the larger
species, the pollen masses may be cut and a portion of it used in
crossing the smaller flower. When the flower of a plant has been
fertilised, the plant should receive special attention; if it is a
Cattleya, Laelia, or one of the large-growing epiphytes, it should, after
the pseudo-bulb bearing the flower has had a number attached to it
corresponding to the number in the stock-book in which the crosses are
recorded, be suspended from the roof in a comfortable and not draughty
situation. If the plant is in a pot, the pot should be placed in a
basket and suspended; or if a suitable position can be found on the
stage, it could be placed on an inverted pot to bring it into prominence
and secure for it careful attention. Where there is a number of
seed-bearing plants, they should be arranged together in the respective
houses in which they are grown.
Early in its development, the seed capsule should be supported by ties,
which, however, should not bring it into an unnatural position, or press
tightly on the part supported. From this time failure may arise from the
conflicting natures of the agents used, or from various causes. Even the
production of a fine and seemingly mature fruit is not a certain
indication of good seeds, for seed capsules have been produced by
irritation of the stigmatic surface by grit or dust, but no fertile
seeds can be thus produced. On approaching maturity, a tie should be
made round the middle of the capsule to prevent loss of seed when the
splitting of the capsule takes place, and, when it is thoroughly mature,
it should be removed, placed in a flower-pot lined with tissue-paper,
and put on a shelf in a dry potting-shed until so thoroughly ripe that
the seeds are being shed in the tissue-paper covering.
At this stage it is possible for the first time to determine whether the
seed, or any of it, is good or not. Examination with a strong lens will
show whether the minute seeds are good or not by the presence or absence
of the embryo in the centre of the elongated covering, which in
imperfectly developed specimens is chaff-like and not thickened in the
middle as are good seeds. Where no good seeds are found, it is the
custom of some growers to discard it at once, and where but few good
seeds appear, attempts are made to discard the chaff and to retain the
supposed good ones for sowing. Where space admits, however, especially
with the beginner, it would be more prudent to sow a portion of the
contents of the capsule, whether supposed to be good or not.
SEED SOWING
A number of the seeds of all seed capsules should be sown as soon as
they are ready, the remainder being carefully stored for sowing later if
required, the seeds sown and those retained being carefully marked with
the number in the record book.
The manner of sowing the seeds varies in different establishments,
satisfactory results having been obtained under very dissimilar
conditions. Failure at first is the usual record of the amateur taking
up Orchid hybridisation, although some few get fairly good success from
the commencement, while those who have had a run of bad luck usually
conquer in the end if they persevere. A scientific reason for some
failures has been given, namely, that an endophytic fungus said to be
necessary to the development of the freshly germinated seeds is wanting
in the early stages, but may be developed naturally after a time, and a
better state of growth result. Be that as it may, it is a curious fact
that the line of demarcation between failure and success in the matter
of raising seedling Orchids is very narrow, and, when the operator
succeeds in raising a fair proportion of the seeds sown, he is generally
surprised at his former want of success, apparently under practically
similar conditions. Formerly the common practice was to sow the seeds on
the surface of the material in which the parent plant was growing, or a
plant of some kindred variety. This practice has been generally
satisfactory and continues in most amateur collections to the present
day. A plant in a basket, or suspended pan or pot, is best, the subject
being chosen for the good quality of the peat, Osmunda fibre, or
whatever material the plant may be growing in. The Sphagnum-moss on the
surface should be clipped very short, the plant thoroughly watered with
rain water, and allowed to drain for a few hours. The seeds should be
sown a few at a time, on the point of a knife or thin strip of hard wood
or ivory, and carefully and evenly distributed over the surface of the
material in which the selected plant is growing. In all cases the number
of the record in the stock-book should be attached, a small celluloid
tablet fastened by a thin wire being the best label, as it is clean and
durable. Hybrids of Laelia, Cattleya, and other true epiphytes should be
suspended in a warm, intermediate house, and Cypripediums and
terrestrial Orchids may be sown in a similar manner in the pots of
either the seed-bearing subject or similar kinds and placed in a moist,
sheltered corner of a house, in which a genial warmth is maintained, the
plants being elevated on inverted flower-pots. Once the seeds are sown,
the plants fostering them should never be allowed to get dry.
Odontoglossum seeds come up best when sown on the surface of established
plants in the manner described. To ensure the best results two or three
sowings of each should be made, and the plants bearing the freshly sown
seeds placed in different parts of the house, some being suspended and
others placed on the stage.
The maintenance of a continual and even amount of moisture after sowing,
and until the seedling plants send forth roots, is of the highest
importance. To water either with a spouted or a rose pot overhead would
wash the seeds away. To avoid this, some resort to the practice of
dipping the plants on which the seeds are sown, allowing the water to
reach only to within an inch of the surface of the compost. This is
better than watering overhead. Spraying with rain-water is an excellent
means of securing uniform moisture, although it requires more care and
attention than dipping. The sprayer is a great help in all stages of
seedling Orchid growth, not only as a means of conveying moisture
direct, but by spraying around the plants and on the staging it is a
great aid to maintaining a moist atmosphere. Let the moisture be
conveyed in whatever manner it may, it must not be forgotten that the
seeds will perish soon after germination if allowed to get quite dry,
either from failure of moisture in the material on which they are sown,
or from an excessively dry air surrounding them. Against the
above-mentioned practice of sowing the seeds on established plants, it
is urged that in that way there is no certain means of keeping the
different crosses from being mixed, by reason of the seeds of one kind
getting into the water-tank and being thus conveyed and mixed with
others; and by seeds falling from plants suspended overhead and coming
up on plants beneath, and in other unexpected places. Such acquisitions,
though often very acceptable, are puzzling, as there is no record of
their origin, or if they come up amongst seeds which have a record, the
chance introductions sometimes have a wrong parentage assigned to them.
[Illustration: PLATE VI
CYMBIDIUM LOWIO-EBURNEUM
(This plant has been commended for its culture on two separate occasions
by the R.H.S.)]
To lessen such risks, it is the custom of some growers to arrange a
seed-raising case, constructed like an ordinary propagating case, in
form like a miniature lean-to, or span-roofed Orchid house. This is
arranged over a part of the staging where there is a slight warmth from
the hot-water pipes. The staging has a few inches of cocoa-nut fibre, or
chopped Osmunda fibre, fine ballast, or other moisture-holding
substance, and on this a number of inverted flower-pots are closely
arranged to form stands for the pots or pans in which the material for
sowing the seeds on is placed: or a light, open wood-work staging is
arranged. The favourite surface for sowing the seeds on is prepared by
stretching a small square of coarse calico or fine light muslin shading
material over a ball of Sphagnum-moss, and pressing it into a 60 or
small 48 size flower-pot, so that the unwrinkled convex surface of the
ball has the centre just below the level of the rim of the pots, the
sides being lower. These are thoroughly soaked and allowed to drain
before sowing the seeds on them, and they are then placed on the
inverted pots in the case. The covering of the case is sometimes of the
nature of hinged sashes to lift from the front, but the most convenient
and best covering is that formed of sheets or panes of glass cut about
one foot wide and of a length sufficient to cover the frame, by resting
one end on a groove in the front side of the case, and the other on the
top bar. A sufficient number of these sheets of glass should be provided
to cover the frame; they are excellent, as they give a certain means of
continual ventilation in some degree through the laps of the glass, even
when closed, and they may be closely or openly arranged to regulate the
amount of air admitted. Such pieces of glass can easily be removed to
inspect the seedlings.
What is commonly called "coddling" causes great mortality among Orchids,
and in this particular the use of seedling cases, if not very carefully
and sensibly worked is less likely to be satisfactory than sowing the
seeds on plants growing in the houses. Too much heat is very harmful.
Odontoglossums proved difficult to raise at first, and this was mainly
because the seedlings were kept too warm and close. If the cultures are
carried on in the Odontoglossum house, success is generally attained,
although the products are seldom so numerous as in Cattleya, Laelia, and
Cypripedium hybrids.
Another plan adopted by some growers, and with tolerable success, is to
place squares of Osmunda fibre in pans, and after soaking them, sow the
seed on them. Others have discs of soft wood, such as Willow, cut across
the grain and placed in flower-pots or pans with the fibre of the
wood-grain uppermost; after soaking the discs, the seeds are sown on
them. When not raised in glass cases, round or square pieces of glass
are placed on the pots. Indeed, there is ample evidence that, provided
good seeds are sown and placed in a suitable temperature, Orchid seeds
germinate readily. The first sign of vitality is given by the good seeds
assuming a green appearance; in time they become little spherical green
bodies, which later produce a growing point; in due course the true root
appears, and the little plants are ready for pricking off or
transplanting into previously prepared store pots prepared with a good
drainage of small crocks or broken charcoal in the bottom, some Osmunda
fibre or other Orchid potting material, and an inch or so of very fine
compost formed of decayed leaves, Osmunda fibre, or good Orchid peat and
Sphagnum-moss in equal parts, the whole rubbed together through a fine
sieve. Some add a proportion of sand to this compost. The whole should
be thoroughly well watered before the tiny seedlings are placed a
quarter of an inch or so apart in small holes in the surface of the
compost and sprayed to settle them in position. Up to this stage the
greatest mortality is observed. Wide crosses between species of
dissimilar nature, and which have up to the production of the growth
point or root appeared to be doing well, having shown that they did not
belong to the unfertile, suddenly collapse. Those which have taken a
long time to germinate have fallen victims to the minute fungi, and
other low forms of vegetable organism, which, commencing at one or two
spots, have gradually overgrown the surface of the pot and destroyed
them. The stronger are often destroyed by small insects, while drip,
however carefully guarded against, claims its share of the spoil. These
things are specially vexing to the amateur who is working in a small
way. To the expert cultivator who has a multitude of subjects in hand,
and whose methods and appliances mitigate the evils, the losses are not
so serious, for when Orchid seeds germinate freely they provide for
losses when sown on a large scale. Nothing is gained by removing the
little seedlings from the seed pot or basket too early. If thriving,
they should be left until they are large enough to be handled safely.
But where there is overcrowding, or "damping off," or decay from fungus,
it is best to remove some or all of the little seedlings in any stage of
growth to the store-pots.
The store-pots should be returned to the seedling case, or placed on a
shelf near the glass in a warm, moist house, where the seedlings should
increase in size until they are ready to remove to fresh store-pots,
when they may be given more room; or if large enough, they may be placed
singly in thimble pots, or three or four seedlings may be placed round
the rims of thumb pots.
Seedling Odontoglossums, when large enough to occupy thimble pots, are
found to thrive well when the pots are fixed in pans or shallow
seed-boxes in Sphagnum-moss, and placed on a shelf near the glass in the
Odontoglossum house, where, like other seedling Orchids, they should be
lightly sprayed several times each day in fine, warm weather, and as
often as may be deemed necessary in colder and dull weather.
From the time the little plants are established in small pots until
their flowering stage, it is only a matter of ordinary culture,
although, as a rule, the small seedlings are safer with four or five
degrees more heat than is afforded the established plants. In the matter
of growth from the seedling stage to the flowering plant, there is but
little need of a resting season, even with species such as are deciduous
when mature, although a diminished supply of water may be given for a
short time to any which, having completed a growth, show no sign of
developing a fresh one. In most cases, a thorough drying, even if it
does not destroy a seedling, causes the flowering season to be delayed
by a year, or even longer.
The careful shading of the seedling house is a very important matter.
Very young plants do best in a subdued light, and until they are quite
strong plants they should not be exposed to direct sunlight. A hot
summer often kills even the plants which have been brought
satisfactorily through a long winter. It is, therefore, advisable to
have on the seedling house, in addition to the lath roller blind,
running on supports carrying it well above the glass of the roof, either
a second lath roller blind running an inch or so above the glass and
beneath the upper one, or a permanent thin cotton shading, which may be
tacked on in spring and left until autumn; or, preferably, so fitted
that it can be rolled up when it is not required.
SELECTION OF SUBJECTS FOR HYBRIDISING
The best varieties procurable should always be selected for hybridising,
it having been proved that crosses originally made with indifferent
varieties are much finer when raised again from more carefully selected
varieties.
There seems to be no certain limit to the possibility of crossing; even
the most dissimilar genera may be crossed with some probability of
getting a successful result.
POTTING MATERIAL FOR HYBRID ORCHIDS
From the time the little plants are well established in single pots, the
same potting material used for all of their kind may be employed, the
plants in the earlier stage having the potting material in a finer
condition than that provided for the larger plants as they approach the
flowering stage.
As with other important operations, in Orchid potting and in the
material used the practice varies considerably, even in the best
collections, and this points to the fact that if the accommodation is
good, the houses properly heated, and other details of culture carefully
carried out, the exact composition of the potting material is of minor
importance. For Cattleya and Laelia hybrids and a large number of
epiphytes grown with them the compost is made by tearing up the
materials with the hand, or in some other way which will not break the
fibres very much. Osmunda fibre forms one-half to two-thirds of the
compost, the other third being made up of good Sphagnum-moss and Oak
leaves or other decayed, dryish leaves. We do not recommend leaf-soil or
leaf-mould, which was formerly strongly advocated, especially by
Continental growers, who used it with disastrous results. The most that
is done now is to mix a proportion of it with other potting material for
Lycastes, Calanthes, Phaius, and similar strong-growing terrestrial
Orchids.
For mixing with the compost for hybrid Orchids, some use crushed crocks,
sand, charcoal, and a small proportion of each or either may be employed
safely, although there is no real need for such materials.
Polypodium fibre may also be substituted for Osmunda fibre, or a
proportion of each may be used. Orchid peat fibre, which used to be the
chief potting material for Orchids, is still perhaps as good as any of
the other fibres, provided a really good quality can be obtained, a
matter which has become increasingly difficult.
For Cypripediums, and especially Selenipediums, a proportion of good,
fibrous loam should be added to the compost recommended for epiphytal
Orchids, the proportion of loam being increased as the plants get
larger. Phaius, Calanthes, Zygopetalums, Zygocolax, and other plants of
a similar character should also have a proportion of loam-fibre in the
compost, and in these cases Orchid peat may be substituted for Osmunda
fibre, if it is of good quality. So far as it has been tested, Osmunda
fibre has an advantage over other fibres, in that it is more durable,
retaining its fibre intact longer than any other. Osmunda fibre and
Polypodium fibre in equal proportions, with an addition of leaves and
Sphagnum-moss, make an excellent material for all young, epiphytal
Orchids, the finer Polypodium fibre, if well worked in, giving substance
to the more open Osmunda fibre.
For very small plants it is well to rub the mixture through a coarse
sieve, but after the early stages the use of the sieve should be
discontinued, and the compost carefully mixed with the hands.