Page:Encyclopædia Britannica, Ninth Edition, v. 18.djvu/285

 VEGETABLE.] PAKASITIS M 267 and Pcronospora parasitica, both occurring plentifully on C rucifcrec, may be mentioned as typical of the group. 1 The Chytridicss, are a small suborder of parasitic fungi inhabiting rarely the epidermal tissue of higher plants, but commonly attacking fresh-water algte and sometimes Infusoria. Many of these exceed ingly simple plants consist merely of a sporangial cell maintained in position and nourishment by a haustorium which penetrates the host cell. The affinities of the group are somewhat uncertain, but probably they are correctly placed among Zygoinycetes. 2 The Uredinex, are endophytic parasites on vascular plants pro ducing the disease popularly called rust. These fungi occur on very various plants, and in their life-history go through a cycle of generations on at least in many cases two different hosts. Corn- mildew is the best known of them, and may be taken as typical of the rest (see MILDEW, vol. xvi. p. 293 ; and for figures, see FUNGUS, vol.&quot; ix. ). This suborder, like the Peronosporeae, is exceedingly destructive to cultivated and other plants. The Rcestelia of the pear tree (which alternates with the Podisoma of junipers) and the P actinia of Malvaccse may be mentioned as familiar examples of the group. The coffee-leaf disease, Hemileia vastatrix, is considered by Ward to be allied to this group. 3 The Ustilagincss are all parasites of a very destructive nature on the stems, leaves, ovaries, &c. , of the higher plants. The mycelial filaments inhabit the tissues of the host, where hypertrophy is FIG. 3. Peronospora parasitica, Dj By. A. Conidiophore with conidia. 15. Mycelium with haustoria (h). frequently set up, and the enlarged space thus obtained is used by the fungus to contain the masses of spores formed by the breaking up of the hyphre. Their whole life-history is carried out in the same host. Though attacking grain crops particularly, many species infest other plants. Ustilayo Carlo, Tul. , is perhaps the commonest, and is exceedingly destructive to a considerable number of grasses. 4 The Entomorjhthorcae, are a very small group attacking insects. The mycelium ramifies densely in the body of the insect and breaks out through the skin where spores are produced singly on basidia. Within the body resting spores are formed by means of which the fungus hibernates. Emimsa MUSC& is very common on the ordinary house fly. 5 1 DC Bary, &quot; Recherchcs sur le developpement do quelques champignons parasites,&quot; Ann. d. Sci. Xat., ser. i-., vol. xx. ; Id., &quot; Zur Kcnntniss der Ferono- sporecn,&quot; in Beitr. zur Morph. u. P/ivsiol. d. I ilze, lift. 2. See also POTATO. 2 Hi aun, &quot; Ueber Cliytridium,&quot; Ac., in Abh. d. Berl. Akad., 185G; Xowakowski, &quot; Beitrag zurKenntnissderChytridiaceen,&quot;in Coin s Beitr. zur JBiol. d. Pjlanzen, ii. ; Do Bary and Woronin, &quot; Beitrag zur Kenntniss d. Chytiidieen,&quot; in Ber. d. Naturforsch. Gesell. zit Freiburg, 1803; Woronin, in Bot. Ztg., 1860. 3 Do Bary, Untersuch. utter die Brandpilze (Berlin, 1853), and &quot; N&quot;eue Untcrsuch. liber Urediueen&quot; in Monatsber. d. Berl. Akad. (18G5) ; Tulasne, &quot;Me m. sur les Uredine es,&quot; &c., in Ann. Sci. Nat., ser. Hi., vol. vii. (Uredin., p. 43), and Ibid., ser. iv., vol. ii. ; Schroter, &quot; Entwickelunctsgesehichte einiger Rostpilzo,&quot; in Cohn s Beitr. zur Biol. d. Pflanzcn, i. ; Ward, &quot; Researches on the Life-History of Hemileia vastatrix,&quot; in Linn. S-jc. Journ. Bat., vol. xix. uber die Brandpilze, Berlin, 1853; KUhn, &quot;Ueber die Art dcs Einchingens der Keimfaden,&quot; &c., in Sitzungtber. d. Naturforsch. Gesellsch, Halle, 1874, and Bot. Ztg., 1874 ; B refold, Bot. Untersuch. uber Hefenpilze, v. 1883. 5 Cohn, &quot; Empufa .l/wsc;e und die Kvankheit der Slubenfliege,&quot; in Kova Ada, xxv.; Brefeld, &quot;Untersuch uber die Entuickelung der E. Muscat und E. radi- cans,&quot; in Abh. d. Naturforsch. Geselhch. Halle, 1871 ; and Ueber Entomoph- thoreen,&quot; &c., inSiteungsber. d. Gesellsch. Naturforsch. Freunde, Berlin, 1877. The Hymenomycctes is the only suborder of Basidiomycctes certainly known to include parasitic members, and these relatively few in number. Agaricus mdlcui, Vahl, by means of its subter ranean mycelium (Rhizomorpha subtcrranca of older authors), is exceedingly destructive to the roots of m;iny trees and woody plants. Other Ayaricini, such as Nyctalis parasitica, attack members of the same group as themselves, but by far the greater number are saprophytes. Trametcs radiciperda, E,. Hart., and T. pini, Fr., Polyponts fulvus, Scop., P. vaporarius, Fr., P. mollis, Fr. , and P. borealis, Fr., all attack Conifers; especially, while P. sulphureiis, Fr., P. iyniarius, Fr., and P. dryadcus, Fr., are parasitic on oaks, poplars, beeches, willows, and other dicotyledonous trees. Tlide- phora, Stereum, and Hydnnm also include species parasitic on trees. 6 The Discomycctcs, like the last group, are mostly saprophytes, but a few distinctly parasitic members are to be found in it. Ascomyccs, Gymnoascus, and Exoascus (E. Priini, Fiickel, and E. deformans, Fiickel) are parasitic, the last- named upon plum, peach, and cherry trees. Several species of Pcziza, as P. calycina, Schum., on the larch, and a number of those belonging to the section of Pseudo- pezizct attack the higher plants. It is highly probable that many Sclcrctia, numbers of them parasitic, the positions of which are not definitely known, will be found to belong to such discomycetous forms as Peziza. Peziza sderotioides, Lib., is said to remain living as a saprophyte after the death of its host. PJiytisma is a very common disease of leaves, such as those of Acer, in which it pro duces large darkly discoloured patches. 7 Pyrenomycetes.Qf this group the Erysiphcee, are perhaps the most destructive as para- sites. They exhibit in their life-history a cycle of generations each of con siderable parasitic activity. The main body of the fungus is commonly epi phytic, the mycelium sending down haustoria through the epidermis of the host (see fig. 4). Of the peritheeial form of fructification good ex amples are Sphserotheca Castcgnei, Lev., the hop mildew (see MILDEW, vol. xvi. p. 294), Phyllactinia, Vncinula, Calocladia, and Erysiphe (E. graminis, Lev., E. Linkii, Lev., E. Martii, Lev., and E. lamprocarpa, Link. ). The oidium forms are also con spicuous as parasites, a familiar example being found in E. Tuckcri, Berk.,. / the vine-mildew (see MIL- FlG&amp;gt; 4__ Erysi pj, e Tudert, Berk. A and B, my- DEW, as above). Clari- celium (?), with haustoria (fi). After De ceps purpurea, Tul., the Bary. ergot of grasses (see ERGOT, vol. viii. p. 251), is the best known and most important of all pyrenomycetous parasites. The group includes a multitude of minor parasites, some of them, however, doubtfully so belonging to such genera as Stiymatca, Sphaerella, Fusisporium, Ramularia, Fumago, Polystigma, Pleospora, Nectria, &c. Nectria ditissima, Tul., is reputed to be the cause of canker in certain trees. Cordyceps is well known as a disease of insects. 8 NATURE OP VEGETABLE PARASITISM. It has been seen that the dependence of parasites upon their hosts for the means of subsistence varies considerably in degree, but it is equally manifest that underlying this condition of existence there are certain facts which char acterize every case. The most important of these is the absence or the inadequate supply of chlorophyll and the 6 R. Hartig, Wiclitige Krankheiten der Watdbdww, Berlin, 1874 ; Brefeld, Botanische Untersuch. uber d. Schimmelpilze, iii. ; and compare also De Bary in Morph. v. Physio!, der Pilze, p. 22. &quot; Willkomm, Die mikroscopischen Ft inde des Waldet, ii. ; Ri-hm, Die Enticickel- Flora, 1877; Ilartig, loc. cit. ; Tichomiroff, &quot;Peziza Kaufmanniana, einc neue aus Sclerotium stammende und auf Hanf schraarotzende Bechei-pilz-Species,&quot; in Bull. Sue. Nat. Moscow, 1868; Brefeld, Bot. L ntersuch. uber Schimmelpilze, Leipsic, iv. Heft, 1881. 8 Tulasne, Selecta fungorum Carpologin, Paris, lSfil-65, and &quot; Me moire sur Ztg. 1SG7.