158 



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 S 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 decomposition 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 

 as 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 

 plants than they could obtain from the soil for themselves. 



HUNGARIAN LOTUS. See Nymphtea ther mails. 



HUNNEMANNIA (named after J. Hnnnemann, a 

 zealous botanist, who died in 1837). OBD. Papaveracece. 

 A. monotypic genus, the species being a very showy, 

 half-hardy, erect-growing perennial, with solitary, ter- 

 minal flowers, and decompound, glaucous leaves. It re- 

 quires a rich soil. Seeds should be sown in spring or 

 autumn, in the open border, and protected during winter. 

 H. fumariocfolia (Fumaria-leaved). /. yellow, like those of 



Eschftcholtzia, californica. July to October. L decompound and 



triternate, glaucous ; leaflets linear, blunt ft. 2ft. to 3ft. 



Mexico, 1827. (B. M. 306L) 



HUNTLEYA. Now included, by Bentham and 

 Hooker, under Zygopetalum (which see). 



HURA (its American name). Sand-box Tree. OBD. 

 Euphorbiacece. 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), fl. reddish, inconspicuous, sterile and 

 fertile on different plants, fr. rounded, hard-shelled, about the 

 size of an orange ; when ripe, and exposed to the action of a dry 

 atmosphere, it bursts with a loud crack, whence the specific name. 

 I. 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). OBD. 

 Cruciferce. A genus limited, by some authorities, to one 

 species; by others, extended to a few allied ones from 

 Southern Europe and Eussian 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. petrsea (rock).* fl. very minute. Spring. I., radical ones pin- 

 nate ; stem ones with fewer and narrower segments, h. Sin. 

 Central and Southern Europe (Britain). A glabrous, delicate, 

 erect annual. (Sy. En. B. 151.) 



HYACINTH. See Hyacintlms. 



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 Peribcea. OBD. Liliacece. 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 iin. 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 

 soil. 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 



