April 13, 1889. 
THE GARDENING WORLD 
513 
ODONTOGLOSSUM ELEGANS. 
In examining the flowers of this supposed natural 
hybrid, and of which we give an illustration, one can 
hardly fail to notice a large weight of characters which 
evidently point to Odontoglossum cirrosum as one of 
the parents. The spotting and large size of the flowers 
are no doubt obtained from 0. cristatum or 0. Hallii. 
The crest is like that of the former. First of all we 
notice that the long, slenderly-pointed, and more or 
less twisted sepals and petals are heavily blotched or 
banded with a rich chocolate-brown on a creamy yellow 
ground. The labellum is yellow at the base, and is 
there shaped exactly like that of 0. cirrosum, while 
the crest is intermediate between the two supposed 
parents. The middle portion is rich brown, and the 
long slender point is white. The slender curved or 
twisted wings of the column are exactly like those of 
the antenme-like processes of 0. cirrosum. A fine 
plant of it was shown by Mr. Ballantine, gardener to 
Baron Schroder, The Dell, Egham, at the meeting of 
the Royal Horticultural Society, at the Drill Hall, 
Westminster, on Tuesday last. It bore a branching 
spike about 4 ft. in length, carrying in the aggregate 
thirty buds and fully-expanded flowers. 
-- 
RUDGEA MACROPHYLLA. 
Seldom are any of the forty-five known species of 
Rudgea known to science seen in 
cultivation, except R. macrophylla. 
This species attains a height of 6 ft., 
but it is probably seldom allowed 
to exceed 3 ft. or 4 ft. in the stoves 
of this country. Tall plants always 
assume a leggy character on account 
of their stiff branching habit, and 
the few side shoots they are dis¬ 
posed to make. For this reason 
alone it is better to propagate occa¬ 
sionally, so as to obtain the requisite 
number of small plants, which flower 
as well and as frequently propor¬ 
tionately to their size as taller 
specimens will. In R. macrophylla 
the axis terminates in an inflores¬ 
cence, and a side shoot develops 
from the axis of one of the upper¬ 
most leaves, and at the time of 
flowering is generally pretty well 
advanced. The flowers are creamy 
white, and developed in dense sub- 
globular heads ; they are fleshy, and 
to all appearance would last a loDg 
time, but they are moreover mod¬ 
erately short-lived. The corollas 
are five or four-parted, even in 
the same head; and the unique 
appearance of the whole inflores¬ 
cence makes the plant worthy of 
cultivation in a collection of stove 
plants. The leaves are in them¬ 
selves ornamental, being large, 
oblong, leathery, and dark green 
with a glaucous hue. A number of plants have been 
keeping up a succession of bloom in the stove at Kew 
for some time past. 
-—- 
DATURA SANGUINEA. 
A large specimen of this planted out in a greenhouse 
or conservatory has a magnificent effect when in full 
flower, which it continues to do in spring for many 
weeks together. Earlier than this, however, it seem 
unable to bloom—at least, in the neighbourhood of 
London. The flower-buds are produced in large 
numbers during winter if the plant is then making 
growth, but they drop off while yet in a very small 
state. The absence of sunshine and the deficiency of 
light have no doubt to account for this state of things, 
and no amount of artificial heat under those con¬ 
ditions would mend matters. Beyond the radius of 
the London smoke, the white-flowered D. suaveolens 
blooms grandly even in mid-winter. The drooping 
trumpet-shaped flowers of D. sanguinea measure about 
7 ins. or more in length, and the tube is orange-yellow, 
almost scarlet, except at the base, where it is tinted 
with green. A well-grown plant has a fine effect when 
studded with these huge drooping funnels. When 
growth becomes played out, the plant ceases to flower, 
and may then be hard pruned back, not only to restrain 
the plant within bounds, but to cause a development of 
strong shoots when the buds break afresh. If planted 
out, no water should be given for some time after 
pruning back. 
THE ATMOSPHERIC CONDI¬ 
TIONS OF PLANT HOUSES. 
( Concluded from p. 449.) 
Referring to the hvgrometrical tables previously men¬ 
tioned, it will be seen that when the dry bulb indicates 
a temperature of 70°, and the wet bulbs the same, the 
air will contain 100 per cent, of moisture—that is, it 
will be saturated ; but if the wet bulb registers 65°, the 
dew point will be 61 T°, and the atmosphere will contain 
73 per cent, of that necessary to saturate it, and so on 
in proportion to the difference between that registered 
by the dry and the wet bulb. Under these conditions, 
there will be no deposit of moisture upon the plants. 
There may be drip from the roof, owing to the fact that 
the air in immediate contact with the glass is cooled 
down to the dew point by the coldness of the external 
atmosphere. That should not affect plants, however, in 
the house, provided means are taken to conduct away 
the condensed moisture. 
Succulent-Plant Houses. 
In the case of succulent plants, it is necessary to main¬ 
tain a more or less arid atmosphere at all seasons, but 
particularly so in winter, when they are or should be 
mostly at rest, or at least growing slowly, and in some 
cases, it may be, flowering. Many of them flower best 
when kept in a dry condition, not only with regard to 
the soil in which they are grown, but also the atmo- 
ODONTOGLOSSUM ELEGANS. 
sphere. Some of them, in fact, refuse to flower at all 
unless they are kept dry and ripened off, as the popular 
expression is, after the completion of their growth. 
During summer, however, when making their growth, 
a great number of them enjoy a liberal supply of 
moisture—more, in fact, than they are generally 
credited with. They will live and make a small amount 
of healthy growth even when kept almost at the point 
of starvation, or what would be certain death to other 
classes of plants which have less capacity for the storage 
and retention of moisture ; but their capabilities as 
ornamental plants are often greatly advanced by their 
receiving liberal treatment during active growth in 
summer. 
Even here the use of the psychrometer would be 
advantageous, and afford an opportunity of making 
many useful observations. A much greater percentage 
of moisture in the atmosphere should be permitted in 
summer than in winter, calculating from the above- 
mentioned facts. During winter the difference between 
the temperatures registered by the dry and wet bulb 
thermometers should be much more marked than in the 
case of other plant houses. The low degree registered 
by the wet bulb thermometer will be a measure of the 
dryness of the atmosphere. Succulent-plant houses 
may be kept at different temperatures, according to the 
nature of their contents, but they should always be 
relatively high in proportion to the degree of humidity 
of their atmosphere. 
Greenhouses. 
Plant houses coming under this heading admit of a 
wide latitude of meaning with regard to the temper¬ 
ature at which they are kept, and the degree of moisture 
in the same, particularly during autumn and winter. 
Houses intended to be kept gay with flowering pdants 
in winter, and which for the sake of distinction may 
be termed conservatories, must be maintained at a 
temperature of from 45° to 50° at night, while those 
intended for the preservation merely of plants from 
frost may be kept at any low temperature, provided 
it is above freezing point, or at least not much below it 
at any time. A much greater amount of moisture may 
be permitted, and is actually necessary where plants 
are to be kept in a growing and flowering condition. 
Even should a cool house be saturated with moisture it 
will actually contain a smaller amount than may be in 
the conservatory, although the atmosphere of the latter 
is considerably above dew point. The fact to be re¬ 
membered here is that the lower the temperature the 
less moisture is necessary to saturate the atmosphere. 
It must not be considered that evaporation ceases at a 
low temperature, and that an excess is impossible under 
these conditions, for, as already mentioned, the tension 
of aqueous vapour is active at all temperatures, and an 
atmosphere at freezing point is capable of retaining 
in solution 5 4 grains of water per cubic metre. 
The damping off of plants or flowers in low tem¬ 
peratures is of frequent occurrence, 
and an evil much dreaded by 
gardeners. During winter the 
atmosphere of this country is 
frequently at saturation point, or 
nearly so, the wet bulb thermo¬ 
meter indicating a difference below 
the dry one of one or two de¬ 
grees, or it may be only from six 
to sixteen-tenths of a degree. Cool 
houses are, or should be, freely ven¬ 
tilated, so that their excess of 
moisture may be dissipated by diffu¬ 
sion into the open air—that is, if 
they contain a greater amount of 
moisture than the external air, 
which they generally do. It is fre¬ 
quently necessary to light the fires 
to drive out the moisture, especially 
during sunless, wet, and foggy times. 
The most fertile causes of damp¬ 
ing are to be found in cool houses 
which are kept at a habitually low 
temperature, and consequently al¬ 
ways on the verge of saturation. 
It is desirable to keep Chrysan¬ 
themums as cool as possible during 
their flowering period in autumn, 
in order to avoid exciting vege¬ 
tative growth, or to prevent its 
becoming drawn and weakly, as 
well as to prolong the flowering 
season as much as possible. Con¬ 
sidering the saturated condition 
of our atmosphere at that period, 
it is not surprising that compact heads of long deli¬ 
cate florets like those of Chrysanthemums should 
be liable to damp in cold moist weather. Like those 
of all other bodies, the thinnest parts, such as the 
florets, soonest part with their heat by radiation, 
bringing the air in contact with them to dew point, so 
that there is a deposition of moisture. Provided this 
were only to last for a short period of time, little harm 
would be done ; but in autumn it may continue for 
many days together. Care should be taken to wipe up 
or drain away all superfluous moisture caused by neces¬ 
sitous watering, and to warm up the hot-water pipes 
occasionally, ventilating at the same time in order to 
dispel moisture. 
Another good illustration of the evil effects of long- 
continued saturation of the atmosphere at a low tem¬ 
perature is sometimes furnished in the case of filmy 
Ferns grown in close-fitting frames or cases, when 
ventilation has altogether been neglected or ignored. 
A heavy dew continually resting upon their thin 
delicate fronds keeps them cold and saturated, and 
prevents transpiration and other necessary functions 
from being performed, till at last the stagnancy of the 
atmosphere reduces the fronds to a black, mouldy, 
decaying mass. In a freer atmosphere they enjoy a 
great amount of atmospheric moisture. 
Fruit Houses. 
Both the temperature and the amount of atmospheric 
