3038 



RUSCUS 



colored sprays (mostly dyed red) are now much used in 

 florists' decorations. 



aculeatus, Linn. Shrub, 1^-3^ ft. high: phyllodia 

 ovate-lanceolate, K-1H in. long, tapering into a spiny 

 point: fls. 1-2, short-pedicelled: berry red, J^in. thick 

 Spring. Gn. 34, p. 231. R.H. 1984, p. 545. Cult, in 

 Fla. and S. Calif. 



R. andr6gynus, Linn.=Semele androgyna, Kunth. R. Hypo- 

 gUssum, Linn., has been highly commended in Germany as a 

 decorative subject. This species and R. HypophyUum, Linn., are 

 both natives of S. Eu., where they have 

 been studied by several botanists, some 

 of whom distinguish them by various 

 characters, while others unite them into 

 a single species. 3. G. Baker considers 

 R. Hypoglossum a variety of R. Hypo- 

 phyllum, differing in having the costa 

 under the cluster of fls. in the form of 

 a large leafy bract lacking entirely the 

 texture of the phyllocladium. In B.M. 

 2049, R. HypophyUum is shown with 

 minute white fls. and handsome red 

 berries nearly J^in. thick. R. racemd- 

 sus, Linn.=Danae racemosa, Moench. 



F. TRACY HUBBARD.! 



RUSH: Juncus. Flowering R. : Buto- 

 mus. R. Lily : Sisyrinchium. 



RUSSELIA (in honor of Alex- 

 ander Russell) . Scrophulariacese. 

 Shrubs with angled, usually slen- 

 der and often pendulous branches, 

 grown in the warmhouse for their 

 * showy flowers. 



3511. RUSCUS aculeatus. Leaves opposite or verticil- 

 late, usually small, reduced to 



scales on the branches: fls. in bracteate dichotomous 

 cymes, either laxly or densely many-fld., sometimes 

 reduced to a single fl., red; calyx deeply 5-cleft or 

 5-parted, segms. strongly imbricate; corolla-tube 

 cylindrical, limb somewhat 2-lipped, 5-cleft, the lobes 

 all rounded; stamens 4, didynamous: caps, subglobose, 

 septicidally dehiscent, valves 2-cleft. About 20 

 species, Mex. and Cent. Amer. A synopsis of Russelia 

 by B. L. Robinson, with a key to the species, will be 

 found in Proc. Amer. Acad. Arts. & Sci., vol. 35, No. 16, 

 March, 1900. 



Russelias are of easy cultivation. R. juncea and its 

 varieties make excellent basket-plants, being almost 

 continuously in bloom. Propagated by cuttings. 



A. Peduncles 1-3-fld. 



juncea, Zucc. (R. scopdria, Hort.). CORAL PLANT. 

 Fig. 3512. A tender shrubby plant, with smooth, 

 somewhat rush-like branches, nodding or pendu- 

 lous at the top: Ivs. linear-lanceolate or ovate, 

 small, becoming minute bracts on the 

 branches: raceme very loose, remotely fld.: 

 peduncles elongated. B.R. 1773. 

 P.M. 4:79. G.W. 5, p. 379. 

 Var. semperflorens, Hort., has 

 been mentioned. Gt. 1:5. 



Lemoinei, Hort. (R. juncea 

 var. Lemolnd, Hort.), is a garden hybrid between 

 R. juncea and R. sarmentosa, said to be more 

 florif erous, especially during the winter, than the 

 parents. 



elegantissima, Hort. (R. juncea var. elegantissima, 

 Hort.), is another product of the same cross as the 

 above and said to have similar characters. 



AA. Peduncles many-fld. 



sarmentdsa, Jacq. (R. multiflbra, Sims). A tender 

 shrub, becoming 4-6 ft. high: Ivs. opposite, ovate, acu- 

 minate, serrately crenate: fls. verticillate, many in a 

 terminal raceme, bright red, erect or drooping about 

 Min. long. B.M. 1528. P.M. 16:163. R.H. 1852:281 

 R ' B - 25:6L F. TRACY HUBBARD.! 



RUSTS 



RUSTS. The plant rusts are fungi constituting the 

 large and well-defined order Uredinales, which con- 

 tains approximately 3,000 species distributed in about 

 forty genera. They are all obligatory parasites, mostly 

 on angiosperms, few on gymnosperms, and a small 

 number on ferns. 



Relations between host and parasite. 



The mycelium of the rust fungi (see Fungi) lives 

 symbiotically within the tissues of the host. It is gen- 

 erally confined to the intercellular spaces, but short 

 branches or haustoria penetrate the cells and absorb 

 nutriment from them. Usually not more than one or 

 two haustoria are found within a single cell and only a 

 small proportion of the host cells are thus invaded, 

 although the mycelium itself is abundant in the inter- 

 cellular spaces. 



The extent to which the mycelium spreads within the 

 tissues of the host and its duration of life vary greatly 

 with different species of rusts. In most of the species 

 which inhabit annual parts of plants, as leaves and 

 stems, the mycelium resulting from individual infec- 

 tions is localized within a more or less restricted area, as 

 in case of hollyhock rust, carnation rust, and wheat rust, 

 and generally persists as long as the infected parts 

 remain alive. That plants thus infected nevertheless 

 become completely covered with rust spots is attribu- 

 table to the large number of separate infections which 

 occur and not to the spreading of the mycelium through 

 the whole plant. When biennial or perennial parts are 

 locally infected, the mycelium often persists for two 

 years, as in the rust of the red cedar, Gymnosporangium 

 globosum and G. juniperi-virginianae, or becomes peren- 

 nial, as in the rust of juniper, Gymnosporangium clavarise- 

 forme, and the blister rust on stems of pines, Perider- 

 mium cerebrum. Many rusts have mycelia which extend 

 throughout the tissues of the host. This type of mycelial 

 distribution is characteristic of the orange rust of the 

 species of brambles, Gymnoconia inter stitialis, and of a 

 number of rusts infecting herbaceous perennial plants, 

 as the rust of Canada thistle, Puccinia suaveolens and 

 the pea rust (Uromyces pisi) on the cypress spurge 

 (Euphorbia Cyparissias) . In such cases the mycelium of 

 the fungus remains dormant in the rhizomes or in the 

 roots and in spring grows out into the developing shoots 

 which are usually characterized by spindling growth 



with long internodes and small and somewhat deformed 

 leaves. Shoots which are normally trailing or prostrate 

 and branches which are naturally horizontal tend to 

 become erect. This effect is sometimes observed in 

 annual plants also, as in the case of Euphorbia maculata 

 infected by Uromyces euphorbise. Blackberry canes 

 growing out from roots infected by Gymnoconia, 

 besides having the characteristic growth described 

 above, are free from thorns. 



In spite of the intimate association of rust fungi with 

 their hosts, very little apparent injury results to the 



