108 
THE DICTIONARY OF GARDENING, 
` HUMUS. The name given to the black substance 
that results from the decay of plants in the soil. Earth 
containing much Humus is often called Vegetable Mould 
or Black Earth, on account of its colour. This sub- 
stance contains all the mineral compounds that existed 
in the living plants, but it chiefly consists of com- 
pounds of carbon, along with oxygen and hydrogen. 
Nitrogen, also, is present, chiefly in compounds of 
ammonia. Decaying organic matter becomes broken up 
into several acids (humic, ulmic, crenic, &c.), which 
have a great power of absorbing ammonia from the air, 
or from its less stable compounds in the- soil, and of 
forming with it substances of greater permanence and 
more suited to yield the nourishment that plants require. 
Hence Humus, which is largely made up of these acids, 
acts an important part in storing up ammonia till re- 
quired by plants; and there seems reason to believe . 
that it may even cause the production of ammonia. by 
decomposing water (H,O), and setting free the hydrogen 
in it, in a state in which it readily combines with the 
nitrogen of the air to form ammonia (H,N), which then 
combines with the organic acids in the soil, Humus 
absorbs water readily, yielding it up as the plants 
require moisture. It has also been suggested that 
it may be of value because of the carbonic acid 
(CO,) formed in and emitted by it; but it is very 
doubtful whether the roots absorb that gas. It is 
certain, however, that the mineral compounds required 
by plants, and present. in their decaying remains, 
are in a state better suited to be absorbed anew 
by growing plants than are the same compounds when 
derived only from the decompvsition of rocks or inorganic 
soils. These properties explain why it is that Humus 
is beneficial to plant life, though, when present in ex- 
cess, e.g., in certain kinds of peat, it renders the soil 
swampy, acid, and unsuitable for the growth of plants, 
except of a few kinds, chiefly rushes, sedges, and 
some grasses, none of which are of any value in cul- 
tivation, The organic matter (so called because it is 
derived from the decay of organised beings, i.e., of 
-~ plants and animals) varies largely in amount in different 
soils. It is composed chiefly of Humus. In very poor 
soils, it may hardly be present at all. Good agricul- 
tural soils contain from 3 to 8 or 10 per cent. of it by 
weight. Old gardens, and other soils that have been 
long under careful cultivation (shown by their dark 
colour), may contain as much as 25 per cent. ; and 
peaty soils may be almost entirely composed of it. 
In the case of ordinary agricultural soils, if the pro- 
duce is constantly removed, and none is returned to the 
soil, the Humus becomes exhausted, or so much diminished 
as no longer to supply the needs of the plants. Therefore, 
it is necessary to replace the missing substances as far 
- a8 can be done; and this is most fully effected by the 
_ use of farmyard manure, in which is contained decaying 
organic matter fitted to restore the Humus that the 
crops have removed. Other manures are frequently em- 
ployed to hasten the decay of plant remains in soil, and 
to increase the amount of Humus thereby; while others 
are added to supply only certain substances in which 
the soil is deficient, or to afford more stimulating food to 
than they could obtain from the soil for themselves. 
HUNGARIAN LOTUS. Sec Nymphea thermalis. 
HUNNEMANNIA (named after J. Hunnemann, a 
—— —— who eng in 1837). ORD. Papaveracee. 
monotypic genus, the species being a very showy, 
half-hardy, erect-growing perennial, with solitary, ter- 
minal flowers, and decomp glaucous leaves. It re- 
quires a rich soil. Seeds should be sown in spring or 
—— in the open border, and protected during winter. 
H, famaricfolia —— yellow, like those of 
zia californica. — L decom —— 
B, g ; linear, blunt. A 2h. to Bit. 
ehoitz 
tauco 
soil. 
HUNTLEYA. Now included, by Bentham and ; 
Hooker, under Zygopetalum (which see). 
HURA (its American name). Sand-box Tree. ORD. 
Euphorbiacee. A genus containing two or three species, 
natives of tropical America; one, H. crepitans, is a 
curious stove evergreen tree, commonly cultivated in 
most tropical countries. Huras thrive in a light loamy 
soil. Propagated by cuttings, inserted in sand, in heat, 
and covered with a bell glass. = 
H., crepitans (crackling). fi. reddish, inconspicuous, sterile and 
fertile on different plants. jr. rounded, hard-shelled, about the 
size of an orange; when ripe, and exposed to the action of a dry 
atmosphere, it bursts with aloud crack, whence the specific name. 
l. glossy, Poplar-like. h. 30ft. to 40ft. 1733. This tree abounds 
in a venomous milky juice. 
HUTCHINSIA (named after Miss Hutchins, of 
Bantry, an accomplished cryptogamic botanist). ORD. 
Crucifere. A genus limited, by some authorities, to one 
species; by others, extended to a few allied ones from 
Southern Europe and Russian Asia, or also to two or 
three perennials from the high mountain ranges of 
Central and Southern Europe. The genus is nearly 
allied to Iberis and Iberidella. The species described 
below is a pretty little subject for the rock garden, or 
for margins or borders, in sandy soil. Propagated by 
divisions, or by seeds. 
H. petræa (rock).* fl. very minute. Spring. l, radical ones pin- 
nate ; stem ones with fewer and narrower segments. h. din. 
Central and Southern Europe (Britain). A glabrous, delicate, 
erect annual. (Sy. En. B. 151) 
HYACINTH. Se Hyacinthus. 
HYACINTHELLA. Included under Hyacinthus 
| (which see). 
HYACINTH, GRAPE. See Muscari. 
HYACINTHUS (the ancient Greek name, used by 
Homer, for the Iris). Hyacinth. Including Bellevallia, 
Hyacinthella, and Peribea. ORD. Liliacee. A genus con- 
taining about thirty species of tunicated bulbous plants, - 
of which three are from tropical and Southern Africa, 
and all the rest natives of the Mediterranean region 
and the Orient. Flowers in simple, lax or dense 
racemes; perianth funnel or bell-shaped, with six 
sub-equal, spreading, erect or recurved lobes; scape 
leafless. Leaves all radical, linear or strap - shaped. 
The very numerous varieties that have originated from 
H. orientalis and H. o. provincialis, are esteemed some of 
the most popular and beautiful of spring-flowering plants 
for indoor and outdoor decoration. By forcing, and care- 
ful management in keeping a succession, Hyacinths may 
be had in flower nearly all the winter, and up till the 
end of May. Nearly all the supplies of new bulbs for 
this and several other countries are obtained from 
Holland. The soil there is sandy, and specially adapted, 
with the climate, to the cultivation of any quantity of 
bulbs. Propagation is effected by seeds for obtaining 
new varieties, and by offsets for perpetuating named or 
distinct kinds. Seeds are seldom sown in this country, 
as most of the new varieties are raised on the Continent. 
If required, they may be sown in light sandy soil, about 
September, covered with din. of’ similar soil, and pro- 
tected throughout the winter. It usually takes from 
four to six years before they reach the flowering stage. 
Offsets should be removed soon after the old bulbs are 
taken up, and be planted out, about 2in. deep, in light 
_ They generally flower the third year. For in- 
creasing a number of offsets of scarce varieties, the Dutch 
growers make one or two cross cuts half-way through 
healthy old bulbs, after taking them up. The following 
year, only a little growth is made above ground, but a 
quantity of young bulbs are formed beneath, which are 
afterwards separated, and planted in nursery beds. As 
the advantages possessed by the Dutch, in raising varieties 
and growing bulbs, are far superior to anything attain- 
able in this country, nearly the whole of the trade is left 
to them, and the produce annually exported in immense 
