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The optimum temperature for sexual reproduction of Phytophthora palmivora (Butl.) Butl., in vitro and in the dark, lay close to 20 °C, whereas that for growth and sporangial formation was 27·5–30°. In contrast, the optimum temperature for sexual reproduction of Phytophthora heveae Thompson, 25°, was also the growth optimum; sporangia were formed only at temperatures above 27·5°. Two isolates of P. palmivora required free water for sporangial formation in the dark. The sporangial morphology of these two isolates also differed in light and dark. Light inhibited oogonial formation and stimulated sporangial formation in both species. An analogy between the effects of temperature and light upon the equilibrium of sexual and asexual processes is suggested. The possibility that responses of the pathogen to the environment in vitro reflect the behaviour of the fungus in nature is also discussed.

The germination of oospores of Phytophthora heveae Thompson, by the production of zoosporangia, on different media, is shown to follow from a period of maturation in the dark followed by exposure to daylight. Germination was also dependent on the nitrogen and carbon source. Similar behaviour is reported for P. cactorum (Leb. & Cohn) Schroet. and for P. erythroseptica Pethybr. except that the latter produces a germ tube only.

In the course of a study of the aquatic Phycomycetes of Illinois which has been in progress during the last several years, eightyfive isolates representing the genus Pythium have been obtained. It was found that these represented sixteen different species, including one whose characteristics are such that it is being proposed as new in the sub-genus Sphaerosporangium. The described species so far recognized in Illinois are as follows: Pythium monospermum Pringsheim, P. dissotocum Drechsler, P. gracile Schenk, P. tenue Gobi, P. catenulatum Matthews, P. torulosum Coker and Patterson, P. inflatum Matthews, P. aphanidermatum (Edson) Fitzpatrick, P. pulchrum von Minden, P. ultimum Trow, P. splendens Braun, P. vexans de Bary, P. cotmplectans Braun, P. debaryanum Hesse, P. irregulare Buisman. The following new species was found

Description Plants attached during early stages of growth, later free floating; holdfast cell elongate obovate, richly lobed; vegetative cell without marked polarity ; distal cell with broadly rounded apex; zoospore globose or imperfectly ovoid. Plants dioecious, nannandrous, idioandrosporous; oogonium 1-9 seriate, terminal or intercalary, depressed globose or depressed pyriformglobose, operculate, division median, wide; oospore globose or rarely subdepressed-globose, filling the oogonium to a fair extent, but not fully ; spore wall smooth ; suffultory cell of the same form as other vegetative cells ; androsporangium two to many seriate ; androspore ovoid ; mature dwarf male almost of the same form as androspore, obovoid, two celled, on oogonium or occasionally on suffultory cells or other vegetative cells ; antheridium internal, antheridial cells 2, lower cell smaller, sterile stipe cell absent ; antherozoid one from each cell, spherical or sub-ovoid ; holdfast (30) 34-40 (44) . wide, (82) 96-I08 (120) long ; vegetative cell (28) 40-48 (52) ?t wide, (64) I10-130 (152) t long; suffultory cell (32) 40-46 (50) p wide, (88) Ioo-I20 (132) p? long ; oogonium (72) 8o-88 (96) [ wide, (60) 64-74 (8o) p long ; oospore (52) 60-64 (72) p. wide, (52) 60-64 (72) V long; androsporangium (24) 28-34 (40) V wide, (8) 10-14 (20) . long; androspore 18-22 p wide, 22-28 p. long ; dwarf male 81-22 p. wide, 22-28 p. long ; antheridium upper cell 18-22 ? wide, 14-16 p. long, lower cell 16-20 p wide, 8-12 p long ; antherozoid I I-I8 p. wide, 12-18 p. long. Parthenospores which are somewhat similar to those described by Mainx (Mainx, 1931) have been repeatedly observed in this species. They are either sub cylindric or cylindric globose (fig. 7,p). The spore completely fills the oogonium in which it is formed and has a reddish brown colour. It contains plenty of stored up food materials and is provided with a smooth thick wall. This alga resembles Oedogonium perspicuum Him (Hirn, I900; Tiffany, 193o) and Oe. confertum Hirn (Hirn, 1900; Tiffany, 1930), both found in Queensland, Australia. The former was also described from KohChang, Siam, under the name Oe. dioicunz Carter (West and West, 1901). The features of similarity include: (I) the operculate nature of the oogonium in which the division is median and wide, (2) the generally globose, smooth walled oospore which is not filling the oogonium, and (3) the general form of the dwarf male. The present alga, however, is

Oospores of Phytophthora palmivora (Butl.) Butl. were formed in host tissue when detached leaves of Piper nigrum were inoculated with an isolate of each compatibility type and incubated at 15–27·5°C in the dark. Oospores were not formed at 30°, and at 22·5° their formation was inhibited by light. Inoculations with single isolates in darkness were sterile. The significance of these observations on the formation of oospores in nature is discussed.

This fungus was obtained from a soil sample l in association with Allomyces. Its more rapid and vigorous growth hindered and at times completely suffocated the Allomyces. In the icebox at a temperature of about 3? C, Allomyces grew slowly but at a fair rate of speed on agar 2 cultures while the Pythium grew very slowly or not at all. However, if the petri-dish cultures were kept at room temperature the Pythium would grow so rapidly as to smother the Allomyces. Because of this variation in growth it was possible to secure pure Allomyces at the lower temperatures and pure Pythium at the higher temperatures. The pure cultures of the Pythium were obtained by cutting out a small portion of agar at the edge of the colony grown under room temperature and transferring the piece to sterile water. After further growth had been established a single sporangium was carried over to a petri-dish containing sterile agar. After 24 hours it would be possible to make further transfers from this growth. Ant larvae and various seeds were used as a supply of food for the fungus. All were attacked by Pythium epigynum. However on ant larvae the hyphae grew longer by about 1-1.5 cm. and very early formed reproductive organs. On hemp seed the 1 The soil-sample was taken from the surface at the waterline of a pond in a meadow near Milton, Wisc. No plants were present; the grass-cover began at a distance of about 3 m.

GERMINATION of comparatively young oospores of Phytophthora erythroseptica has been obtained following passage through the digestive tract of the garden snail, Helix aspersa. These oospores were produced in oat agar cultures maintained at 20° C. for 4–6 weeks. Portions of the culture were fed to snails, and the excreta collected and kept in a moist atmosphere at room temperature. The old oogonial and antheridial walls appeared unaltered by this treatment, and within a few days germination of a number of oospores was observed.

Isoachlya luxurians sp.nov. is characterized by large eccentric oospores, usually only one in each oogonium, and the presence of antheridia. Sex organs are produced early and abundantly after luxuriant growth at 22–25° C.

The mating type behaviour of 176 single zoospore isolates collected from 11 dissected sporangia of Phytophthora cinnamomi Rands was examined and the results confirmed previous conclusions from studies of field isolates, that two compatibility types may be involved in the formation of oospores in this fungus. The bilateral formation of sexual spores in paired cultures is believed to occur via the hyphal fusion of two compatibility types and it is thought that chemical stimulation is not involved. Oospore production is also affected by nutrition and innate characters of the isolates used. Determination of the mating reactions of terminal hyphae isolated from mixed A1 and A2 cultures suggested that extensive heterokaryosis of A1 and A2 type nuclei did not occur in the vegetative hyphae of either mating type, and that heterokaryon formation was probably restricted to the site of oospore formation. The absence of 'vegetative' heterokaryosis between the two mating types of P. cinnamomi is postulated and the control of sexuality in this fungus is discussed.

Pythium dimorphum, a new species, is characterized by oogonia partially to completely covered with blunt irregularly spaced projections averaging 3 / in length and aplerotic to nearly plerotic oospores averaging 30 / diam. Antheridia may be hypogynous or monoclinous but are frequently absent. Prominent ovoid to elongate thin-walled, spherical chlamydospores averaging 64 L in diam with dark contents are a distinguishing feature of this fungus. Ovoid or club-shaped sporangia, averaging 28 X 54 1A, are present.

Using a slide-culture technique examination of four strains of Phytophthora cinnamomi and five of P. cryptogea, growing in pairs, has shown that hybridization takes place, P. cinnamomi forming the antheridium and P. cryptogea the oogonium. Later, some of the cinnamomi isolates form non-hybrid oospores, apparently stimulated by conditions in the dual culture. A sixth cryptogea strain produces oospores when grown with members of either species.

During the course of a study of an isolate of Chvtriomyces hyalinus Karling (5) the sporangia of this chitinophyllic fungus became heavily infected with two other chytrids. The first of these parasites to be reported here relates to the eucarpic. rhizidiaceous genus Rhizophydium. It occurred first in great abundance on a pure culture of C. hyalinus which was growing on purified shrimp chitin. but later a few of its thalli were found on C. aureus also. In view of the latter discovery, inoculation tests were made at once to determine whether or not this fungus will infect other chitinophyllic chytrids. Heavily infected sporangia of C. hyalinus were repeatedly introduced into cultures of Asterophlyctis sarcoptoides, Siphonaria variabilis, Obelidium mucronatum, Chytriomyces appendiculatus, Rhizophlyctis petersenii, Polychytrium aggregatum, and Rhizidium sp., but none of these chytrids became infected. Likewise, cultures of Achlya flagellata, Saprolegnia ferax, Aphanomyces sp., and various species of Pythium were inoculated in the same manner, but no infection occurred. These results suggest that the parasite may be limited in host range to two species of Chytriomyces. It is significant to note that it has not infected C. appendiculatus, another chitinophyllic species of Chvtriomvces from Virginia and Connecticut. So far only six, or possibly seven, Rhizophydium parasites of other fungi have been reported: R. carpophilum on various aquatic Oomycetes (Zopf, 12, and others), R. (Mastigochytrium) Saccardiae on the ascocarps of Saccardia Durantae (Lagerheim, 6), R. Pythii on Pythium complens (de Wildeman, 10), R. fungicolum on the hyphae of Gloeosporium (Zimmerman, 11), R. pollinis on conidia of Sclerospora graminicola (Muller, 8) and oospores of Albugo bliti (Melhus, 7), R, parasitans on Rhizophydium gonio

The soil-borne fungus Phytophthora cinnamomi Rands is a particularly impor-tant pathogen in Australia because of its consistent association with root-rot disease of a wide variety of exotic and native plant species. It was thought originally to have been introduced from south-east Asia (Crandall and Gravatt 1967), but evidence recently obtained (Pratt, Heather, and Shepherd, unpublished data), suggests that it may be indigenous to eastern Australia and may have been partly instrumental in determining the distribution of certain susceptible species, particularly Eucalyptu8 spp.

The information available regarding the survival of freshwater algae during dry periods is somewhat meagre. Text-books (Fritsch 1935; Smith 1938, 1951; West & Fritsch 1927) refer to 'resting cells', 'cysts', 'akinetes' and 'resistant stages' but with some exceptions little appears to be known in detail about the droughtsurvival value of these stages. Physiologically, a cell or a group of cells in which growth has ceased, temporarily at least, and in which the metabolic processes are at a minimum may be said to be a resting stage. This is a wide definition and includes such structures as resting oospores, zygospores, hypnospores and akinetes. For each algal species one or more of these stages might assist in the survival of the species during dry conditions. Str0m (1924), referring to the overwintering of algae, said that the importance of zygospores and other resting spores had been greatly exaggerated and also pointed out that it is incorrect to generalize, as species of a genus may differ widely in their reactions to any particular condition. Bristol (1920) found that algae surviving in old stored soils (26-73 years old) included members of the Cyanophyceae, the Chlorophyceae and one diatom, Nitzschia palea. Certain terrestrial algae have been investigated with regard to the survival of vegetative stages during drought by Fritsch (1922) and Fritsch & Haines (1923). Various references have been made to the accumulation of granular bodies or oil globules in organisms exposed to periods of desiccation (Denffer 1949; Fritsch 1916, 1944; Heide 1939; Kahn 1949; Petersen 1935; Piercy 1917; Salah 1952). Rao (1953) carried out some work on the algae of a pond which eventually dried up but he found no resting stages. Lund (1942) observed an immediate decrease in the algal flora of exposed pond-bottom deposits when the surface of the mud areas began to dry, but found no stages of the normally aquatic algae which he could

ATTENTION was directed in NATURE of April 30, 1914 (vol. xciii., p. 226), to the discovery of a rather remarkable mode of development of sexual organs which occurs in certain species of Phytophthora, and was first found in P. erythroseptica and then in P. infestans, the "potato-blight" fungus. Several other species of the genus are now known to produce sexual organs in this novel fashion, in which the oogonial incept penetrates the antheridium at an early stage, traverses it, emerges, and then swells to form the oogonium proper within which the oospore ultimately develops. It was suggested then that those previously well-known species (such as P. cactorum, etc.) in which the antheridium and the oogonium lie side by side, and penetration of the latter by the former occurs laterally, should be excluded from the genus Phytophthora and be placed in a new one, Nozemia. A species (from decaying apples) has now been isolated by Mr. H. A. Lafferty, working here, in which the sexual organs are developed mainly according to the Nozemia type, but occasionally and simultaneously in the same individual according to the Phytophthora type, with amphigynal antheridia. This species, therefore, forms a connecting link between the two groups; and it would seem no longer necessary or desirable to retain the generic name Nozemia.