CHAPTER V. —COMPARATIVE REVIEW — ANCYLISTEAE. 139 



gonidia, but does not produce oospores. This may occur in all species ; and among 

 those which have been more thoroughly examined there are two, Phytophthora 

 infestans and Pythium intermedium, which, as far as accurate observation extends, 

 have lost the power of forming oospores, and produce gonidia only (see p. 125). 



Literature of the Peronosporeae. 



De BarY, Recherches sur le developpement de quelques Champignons parasites (Ann. 

 d. sc. nat. se'r. 4, XX, where the older literature, especially Tulasne's works, is 

 cited;— Id. Beitr. z. Morph. u. Phys. d. Pilze, II;— Id. Beitr. IV, Unters. ii. 

 d. Peronosporeen u. Saprolegnieen, &c. ; — Id. Zur Kenntn. d. Peronosporeen 

 (Bot. Ztg. 1881). Further notices of works are given in the two last-mentioned 

 treatises. 



Pringsheim in Jahrb. f. wiss. Bot. I (Pythium). 



M. CORNU, Monographie des Saprolegniees (Ann. d. sc. nat. ser. 5, XV, 1872) ;— Id. 

 in Comptes rendus, XCI and XCII, 1880, 1881 ;— Id. Observations sur le Phyl- 

 loxera et les parasitaires de la vigne. Etude sur les Peronosporees, II. Le 

 Peronospore des vignes, Paris, 1882 (Acad.). 



SCHROTER, Peronospora obducens (Hedwigia, 1877, p. 129) ;— Id. Protomyces grami- 

 nicpla (Hedwigia, 1879, p. 83). 



Farlow, On the American Grape-vine mildew (Bullet, of the Bussey Institution, 1876, 

 p. 415). 



A. Millardet, Le Mildiou, Paris, G. Masson, and in Journal d'Agriculture pratique, 

 1881, I, No. 6, and 1882, II, No. 27. 



A. ZALEWSKI, Zur Kenntn. d. Gattung Cystopus (Botan. Centralbl. 1883, No. ^). 



ANCYLISTEAE. 



Section XXXVIII. The Ancylisteae are a small group of small plants, 

 parasites on fresh water Algae and nearly related to the Peronosporeae and especially 

 to the genus Pythium. The tubular thallus is at first unsegmented in all the 

 members of the group and is divided into cells by transverse walls for the purpose of 

 forming oospores ; some of these cells swell into vesicles and become oogonia, the 

 rest continue narrow and answer to the antheridia of Pythium. The two kinds of 

 organs either lie side by side in the monoecious thallus, somewhat as in Fig. 67, as is 

 the case in Myzocytium globosum of Cornu ; or they are dioeciously distributed, some 

 plants forming only oogonia, others only antheridia, and the antheridia send out a 

 tubular filament by means of which they unite with the oogonia, as in Lagenidium 

 Rabenhorstii of Zopf, which lives in Spirogyra, and in Ancylistes of Pfitzer, a parasite 

 on Closterium. In these plants there is no distinct differentiation of oosphere and 

 periplasm previous to the formation of oospores ; it appears, on the contrary, that the 

 partition-membrane between the antheridium and oogonium is first perforated, and 

 the whole of the protoplasm of the antheridium passes into the oogonium, and it is 

 not till then that the combined protoplasm withdraws from the wall of the oogonium 

 and developes into the spherical thick-walled oospore. The more special structure of 

 the oospore varies with the species. Their germination has not been observed. No 

 organs are known in Ancylistes Closterii except those just mentioned, the propagation 

 of the plant being effected by the thallus-tubes growing from one closterium-cell to 

 another and forcing an entrance into it. The other forms named above produce 

 zoospores after the manner of Pythium, and from sporangia which originate like the 

 oogonia by transverse segmentation of die thallus. The group requires more 



