492 



DIBCA 



DISEASES 



DlKCA (Greek, from dirke, a fountain; referring to 

 the plant as growing in moist places*. Thymelcedcece. 

 Two species of North American shrubs, with tough, 

 fibrous bark, alternate, thin, short, entire, petiolate, de- 

 ciduous Ivs., apetalous perfect fls. in peduncled fascicles 

 of the previous season's growth, the branches develop- 

 ing subsequent! y from the same nodes : calyx corolla-like, 

 yellowish, campanulate, undulately obscurely 4-toothed, 

 bearing twice as many exserted stamens as its lobes 

 (usually 8) : ovary nearly sessile, free, 1-loculed, with a 

 single hanging ovule; style exserted, filiform: fr. berry- 

 like, oval-oblong. Hardy deciduous branching shrubs, 

 often with the habit of miniature trees. Bark of inter- 

 laced, strong fibers, and branches so tough and flexible 

 that they may be bent into hoops and thongs without 

 breaking. So used by tne Indians and early settlers. 

 The Leatherwood is not one of the showiest of hardy 

 shrubs, but its small, yellowish flowers are abundant 

 enough to make it attractive, and it deserves cultivation 

 especially for the earliness of its bloom in spring. It is 

 of slow growth, and, when planted singly, makes a com- 

 pact miniature tree; planted in masses or under shade 

 it assumes a straggling habit. It thrives in any moist 

 loam. Prop, by seeds, which are abundant and germi- 

 nate readily: also by layers. 



720. Leatherwood Dirca palustris (X 



paliistris, Linn. LEATHERWOOD. MOOSEWOOD. Pig. 

 720. A shrub, 2-6 ft. high, with numerous branches 

 having scars which make them appear as if jointed, at 

 the beginning of each annual growth, and with yellow- 

 brown glabrous twigs: Ivs. oval or obovate, with obtuse 

 apex, 2-3 in. long, green and smooth above, whitish and 

 downy below, becoming smooth, the base of the petiole 

 covering buds of the next season: fls. yellowish, abun- 

 dant enough to be attractive, nearly sessile, %in. long, 

 falling as the Ivs. expand: fr. hidden by the abundant 

 foliage, egg- or top-shaped, % in. long, reddish or pale 

 green. Woods and thickets, mostly in wet soil N. and S. 

 B.R. 4:292. Common. 



D. occidentdlis, A. Gray. A similar species found on the Pacific 

 coast, differs mainly in the deeper calyx-lobes, lower insertion 

 of the stamens, sessile flowers, and white involucre. Not in the 

 trade, hut worthy of cult. A. PHELPS WYMAN. 



DISA (origin of name unknown). Orchidctceoe, tribe 

 Ophrydece. One hundred or more terrestrial orchids, 

 mostly S. African, of which several are known to fan- 

 ciers, but only one of which is in the Amer. trade. 

 Sepals free, spreading, upper one galeate, produced in a 

 horn or spur at the base; petals inconspicuous, small, 

 adnate to the base of the column. The species described 

 below is undoubtedly one of the most beautiful of known 

 orchids, but as yet difficult to manage under artificial 

 conditions. 



grandifldra, Linn. FLOWER OF THE GODS. Rootstock 

 tuberous: stems 1 ft. or more high, unbranched: Ivs. 

 dark green: fls. several; upper sepal hood-like or gale- 

 ate, 3 in. long, rose-color, with branching crimson veins; 

 lateral sepals slightly shorter, brilliant carmine-red; 

 petals and labellum orange, inconspicuous. S. Afr. 

 B.M.4073. G.C. II. 18: 521; 111.9:365. OAKES AMES. 



William Watson, in Garden and Forest 9: 284, says of 

 Disa : "They all require cool-greenhouse treatment, 

 plenty of water, an open, peaty soil and shade from direct 

 sunshine. As soon as the plants have flowered, they are 

 shaken out of the soil, the suckers taken off, and potted 

 singly in small pots and watered liberally. In November 

 they are again potted into 3-inch pots, in which they 

 remain until they flower. They make a display of flowers 

 for about two months." In G.F. 7: 324, Watson writes of 

 D. Kewense: "This is a beaxitiful hybrid, which is as 

 easily grown as any orchid I know of, and multiplies 

 itself by means of offsets with all the prodigality of 

 Couch Grass. Many connoisseurs declare it is the best 

 of all Disas. ***!>. Veitcliii is a noble plant, and 

 almost as free as D. Kewense. I would recommend all 

 growers of orchids to procure both and propagate them 

 as rapidly as possible. * * * The Kew plants are in 

 4-inch pots, and each bears a spike 18 inches high with 

 from 10 to 20 flowers, each 2 inches across." For portrait 

 of D. Kewense, see G.C. III. 18: 273. 



DISANTHUS (Greek, dis, twice, and anthos, flower; 

 the fls. being in 2-fld. heads), ffamameliddcece. Shrub,, 

 with alternate, deciduous, entire, long-petioled Ivs.: fls. 

 similar to those of Hamamelis, but borne in pairs on 

 erect axillary peduncles and connate back to back: cap- 

 sule 2-celled, with several seeds in each cell. The only 

 species, D. cercidifdlius, Maxim., is a shrub, with slender 

 branches, 8-10 ft. high: Ivs. roundish-ovate, palmately 

 nerved, 3-4 in. long: fls. dark purple, in October. G.F. 

 6:215. Hardy ornamental shrub of elegant habit, with 

 distinct, handsome foliage, turning to a beautiful claret- 

 red or red and orange in fall. Prop, by seeds, germi- 

 nating very slowly, and by layers ; probably also by 

 grafting on Hamamelis. ALFRED REHDER. 



DISEASES of plants are of many classes. The word 

 disease as applied to plants is commonly associated with 

 those manifestations which are the result of seriously 

 disturbed nutrition, rather than with mere attacks of 

 devouring insects. We might classify diseases, for hor- 

 ticultural purposes, as those due to parasitic fungi (or 

 fungous diseases), those due to bacteria or germs, those 

 due to nematodes or eel worms,. and those which are as- 

 sociated with disturbed or imperfect nutrition. To 

 these four classes we shall now give our attention: 



FUNGOUS DISEASES are those that are due to the inva- 

 sion of tissue by fungi (see Fungus). All crop plants 

 are more or less subject to the attack of these insidious 

 foes, and the havoc they bring is rarely fully appre- 

 ciated. 



The chief lines of treatment with plants subject to 

 injury from fungi are, first, to reduce the number of 

 spores to a minimum, and, secondly, to surround the 

 plants with conditions unfavorable for their develop- 

 ment and yet not to interfere with the growth of the plant 

 itself. Fungi as a rule are fond of moisture and, there- 

 fore, dry weather is an ally of the cultivator, while a sea- 

 son with high humidity and a large rainfall is asso- 

 ciated with an abundance of plant diseases. So long, 

 therefore, as the weather is without man's control there 

 will be an uncertain quantity in the problem of plant 

 healthfulness. 



The growing season for crop plants is practically the 

 same as that for fungi, and during the winter inactivity 

 prevails for both host and parasite. In other words, 

 there are several months of the year when the fungi are 

 either inactive in the host plant or lying dormant out- 

 side of it, ready to begin their destructive work. When 

 the plant is a perennial, the fungus may live over winter 

 in its tissue, as is well illustrated in the black-knot, Plow- 

 rightia morbosa, of the plum and cherry. The swellings 

 upon the twigs increase from year to year until the stem 

 is girdled or otherwise destroyed. The fungus is peren- 

 nial, and every knot, unless the branch is dead, is the di- 

 rect starting point for new growth. Along with this 

 fact is the equally important one that in the hard, black 

 crust of the excrescence there are innumerable spheri- 

 cal pits in which countless spores pass the winter, and 

 are ready to spread the disease to new, healthy twig* as 

 the knot breaks up and fresh growth starts in the tree 

 in spring. In the light of the above facts there are 

 many reasons for destroying the knots upon a plum or 



