DISA 



ceolate. S. Afr. Gn. 73, p. 187. D. 6lwesii, Hort. A garden 

 hybrid, probably between D. kewensis and D. Veitchii. D. eques- 

 tris, Reichb. f. Dorsal sepal funnel-shaped, pale blue; petals white. 

 Rhodesia. D. erubescens, Kendle. Fls. large and handsome, some- 

 what resembling D. grandiflora in color. Trop. Afr. D. kewinsis, 

 Hort. Hybrid between D. grandiflora and D. tripetaloides. Spike 

 few-fld. ; fls. 1 j/zin. across; lateral sepals rosy pink, the dorsal paler, 

 red-spotted; lip yellowish, crimson-spotted. Gt. 52:1510. O.R 

 6:24; 9:273; 20:336. D. longicornu, Linn. f. Plant Y r \ ft. 

 high, producing a single fl. about 2 in. long resembling a light 

 blue delphinium. S. Afr. D. litgens, Bolus. Spike 10-15-fld.; fls. 

 dull purple, the lip green, lacerated. S. Afr. B.M. 8415. D. Lima, 

 Hort. A garden hybrid between D. racemosa and D. Veitchii. 

 D. pulchra, Sond. Spike 6-12 in. long; fls. rose. S. Afr. G. 28: 

 201. D. racemdsa, Linn. f. Racemes 4-9-fld.; fls. deep rose-red, 

 about \Vi in. across. S. Afr. B.M. 7021. J.H. III. 47:213. D. 

 sagittjlis, Swartz. Fls. in a short raceme, about 2 'sin. long, pale 

 lilac, the petals and lip red-streaked. S. Afr. B.M. 7403. G.C. III. 

 51:312. D. Veitchii, Hort. Hybrid between D. racemosa and D. 

 grandiflora. Fls. about 2 % in. across, rose-lilac. J.H. III. 43:145. 

 C.O.I. O.R. 6:241; 9:273; 20:336. D. venusta. Bolus. A slender 



GEORGE V. 



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

 the fls. being in 2-fld. heads). Hamamelidacex. Orna- 

 mental shrub, grown 

 for its handsome foli- 

 age, assuming beauti- 

 ful autumnal tints. 



Deciduous, glabrous : 

 Ivs. alternate, long- 

 petioled, entire, pal- 

 mately veined : fls. per- 

 fect, axillary, in pairs 

 on erect peduncles and 

 connate back to back; 

 calyx 5-parted; petals 

 5, spreading; stamens 

 5, snorter than sepals; 

 ovary superior, with 2 

 short styles: fr. a dehis- 

 cent caps, with several 

 black glossy seeds in 

 each cell. One species 

 in Japan. Hardy orna- 

 mental shrub of ele- 

 gant habit, with dis- 

 tinct, handsome foli- 

 age, turning to a beauti- 

 ful claret-red or red and 

 orange in fall. Prop, 

 by seeds, germinating 

 the second or thirc 

 year, and by layers; 

 possibly also by graft- 

 ing on Hamamelis. 



cercidifdlius, Maxim. 

 Fig. 1278. Shrub, to 

 10 ft., with slender 

 branches: Ivs. round- 

 ish - ovate, obtuse or 

 acutish, truncate or cordate at the base, leathery at 

 maturity, dark bluish green above, paler below, 2-4 in. 

 long: fls. dark purple, about %in. across, with linear- 

 lanceolate petals. Oct.: fr. ripens the following Oct. 

 High Mountains of Cent. Japan. G.F. 6:215 (adapted 

 in Fig. 1278). R.H. 1910:363. Demands a light peaty 

 8 il- ALFRED REHDER. 



DISEASES AND INSECTS. Under one head it is 

 thought best to bring together the discussions of the 

 so-called enemies of plants, the parasitic fungi and 

 the depredating insects, together with the means of 

 control. This composite article therefore comprises: 



Page 



Diseases due to parasitic fungi 1021 



Fungicides, or remedies for these diseases 1027 



Catalogue of diseases, with advice 1029 



Insects and their depredations on plants 1034 



Insecticides and fumigation 1042 



Catalogue of insect depredators, with advice 1047 



Spraying 1057 



1278. Disanthus cercidifolius. 



DISEASES AND INSECTS 1021 



The reader now has before him a comprehensive 

 survey of the subject. It is impossible, of course, to 

 list all the plant diseases and all the insect pests in a 

 compilation of this kind; but it is desired that the 

 catalogues shall comprise the most important depreda- 

 tors of the leading horticultural plants. The reader 

 should keep himself informed of the new knowledge and 

 new practice by consulting current publications of the 

 government and the experiment stations. 



Diseases of plants. 



Disease in plants may be denned as any derangement 

 or disorganization of the normal structure or physio- 

 logical functions of the plant, as for example the for- 

 mation of galls, cankers or distortions, rotting of plant 

 parts, or disturbances in the sap system resulting in 

 wilting, or in the nutritive processes resulting in such 

 symptoms as dwarfing, chlorosis, and the like. Forma 

 of plant diseases are shown in Figs. 1279-1292. 



It is often very difficult to distinguish clearly between 

 diseased conditions and abnormalities of other types. 

 Bud-sports, doubling of blossoms, fasciations and many 

 other similar abnormalities, 

 while often the result of reac- 

 tion to some pathogen, are 

 not apparently always so and 

 they are often spoken of as 

 teratological phenomena. 

 While the reaction of plants 

 to insect attacks in the forma- 

 tion of galls, cankers, and so 

 on, is to be regarded as symp- 

 tom of disease, the injuries 

 produced by the mere eating 

 away of parts of leaf, stem or 

 fruit are not usually so to be 

 regarded. Even here, how- 

 ever, it is often difficult to 

 draw a sharp line of demar- 

 kation. While disease may 



usually be said to result in ultimate injury, there are 

 apparently certain marked exceptions, as in the case of 

 the root tubercles of legumes caused by the attacks of cer- 

 tain nitrogen-fixing parasitic bacteria. Here increased 

 growth and crop-yield are generally held to result. 



Diseases of plants are not something new or of 

 recent development, as the grower is often inclined to 

 think. The crops of the husbandman, from the earliest 

 recorded history of his art, have been afflicted with 

 diseases. In the historical writings of the Hebrews, the 

 Bible, and in the writings of the Greeks and Romans, 

 frequent mention is made of such diseases as rusts, 

 smuts and mildews of grain and canker of trees. To be 

 sure, the extensive and intensive crop-cultivation of 

 modern times, tqgether with the extraordinary world- 

 wide transportation and exchange of crop-products, 

 have greatly favored the distribution of plant pathogens 

 (insects, fungi and bacteria), and afford them excep- 

 tional opportunities for destructive development. Nor 

 are cultivated plants alone subject to disease. Disease 

 epidemics among weeds and the wild flowers of the 

 woods may be observed any season in localities in 

 which weather conditions especially favor the causal 

 organisms. 



The study of the nature and control of plant diseases, 

 however, is of recent development. The first man 

 really to study plant diseases from the true modern 

 economic point of view, that is, with the object of help- 

 ing the grower to understand and combat or control 

 diseases m his crops, was Julius Kiihn. This German, 

 the son of a German land-owner and for many years 

 himself the manager of a large agricultural estate, was 

 the founder of an early German agricultural college. 

 He interested himself, among other phases of agri- 

 culture, in plant diseases and their control and his 



