thiamine, pyridoxine, nicotinic acid, folic acid, ascorbic acid. Without thiamine practically no growth of the fungus took place ; omission of pyridoxine had nearly as adverse an effect. Raffinose and cellobiose were the best carbon sources ; glucose also gave a good yield of mycelium. Statistical analysis of factorial experiments indicated that a correct balance between the mineral constituents of the medium and between the carbon and nitrogen sources is essential in order to obtain a high yield of mycelium.Apple scab is one of the commonest orchard diseases in temperate regions. The disease attacks all parts of the tree and when infection of the fruit is severe the yield of marketable apples may be decreased by as much as 50 yo.This disease is caused by the fungus Venturia inaequalis (Cooke) Winter, an . ascomycete. The conidial phase, which is the more important stage from a pathological standpoint, was a t one time called Fusicladium dendriticum (Wallr.) Fol.; this stage is found on all living parts of the host. The perithecial stage is less noticeable and occurs only on over-wintered fallen leaves. Most of the work done on Venturia inaequalis in the past has concentrated on the genetics of disease resistance and susceptibility. Johnstone (1931) suggested that resistance to the fungus was not due to any single factor and appeared to depend on the physiological relationship between host and parasite, while the work of Keitt & Langford (1941) indicated that it might be connected with the nutrition of the fungus. The nutritional requirements of V. inaequalis have not previously been comprehensively investigated; the present paper describes results of work along these lines. lMETHODSStock cultures of Venturia inaequalis were grown on malt-extract agar slopes containing apple leaf decoction; this MEAL medium was prepared as follows. Air-dried 'Bramley's Seedling' apple leaves (25 g.) were boiled in 500 ml. distilled water for 30 min. Malt extract ( 5 g.) and agar (25 g,) were dissolved in distilled water and the filtered leaf decoction added to this mixture, which was then made up to a final volume of 1 1. The inoculum for all experiments was prepared by adding 15 ml. sterile distilled water to a 6 x 2 in. tube 26 G. Microb. XII

SUMMARYNutritional experiments were carried out dealing with : (1) the utilization of sulphur compounds; (2) the action of different mineral salts and their interaction. The results showed that the species of Pythium used grew well a t 28O buffered with Sorensen's salt to give an initial pH of 6-5 and incubated for 13 days for Pythium afertile and 10 days for the remaining species. Acid conditions below pH 5.0 and alkaline conditions above pH 8-0 were not tolerated. The best carbon and nitrogen sources are given. The best sulphur sources were Na,S, Na2S,0,, Na,SO,. 10 H20, Na,SO, . 7H20, Na,S,O,. 5H,O, K2S20a, molecular sulphur, m-methionhe, thioacetamide, L-cysteine, sodium thioglycolate, and DL-cystine Factorial experiments were carried out in which the fungi were incubated at 28' for 13-14 days. Statistical analysis of the results showed that under the given conditions optimal growth measured as mg. dry wt. was obtained in liquid media containing glucose, 10.0 g. 11. ; KC1, 0-5 gJ1. ; with varying amounts of K,HPO,, KNO, and MgSO, . 7H,Ofor the different species specified. There was a balance between K2HP0, and MgSO, . 7H20 for P. debarya w m and there were significant interactions between the salts above taken two at a time for P . debaryanurn and P . ultimum but the interactions for the remaining fungi were more variable. There was interaction between all three salts together for two of the species. P . debaryanum is more exacting in its nutritional requirements than the other species.Some species of Pythium are purely saprophytic, others are normally parasitic but may be saprophytic. Thus Pythium would seem to be a good genus for comparative nutritional studies. Previous work a t Newcastle upon Tyne (see Fothergill et al.) indicated that for some parasitic fungi the balance of the major inorganic salts in a culture medium was more important for the good growth of the mycelium than the concentration of individual salts, but in the case of some saprophytic species, the balance of salts was much less important. Results, however, over a range of fungi varied. The present experiments are a continuation of work designed to investigate these points. Excluding work done on Pythium as a plant pathogen, a few physiological investigations have been reported mainly dealing with the presence and function of pectinase in these fungi (

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SUMMARY: A series of four factorial experiments with culture media was carried out dealing with (1) the action of individual salts and their interactions in the medium, (2) the relation of the nitrogen source to the action of the salts, (3) the effect of the ratio of the carbon source and (4) the proportionate influence of the salts in the medium. Statistical analysis of the results has shown (a) the composition of the culture medium which produces optimal growth under given conditions, (b) that a suitable balance of salts in the medium, while conducive to good growth, is not of over-riding importance to this fungus, and (c) that ammonium nitrate serves as the key nutrient in the balance of salts which produces optimal growth measured as milligrams of dry weight.The real study of the nutrition of fungi probably began when Raulin introduced his defined medium in 1869. Since that time there have been numerous accounts of, and references to, fungal nutrition, but there is a lack of statistical investigations of the food requirements of fungi which are complete from one aspect of nutrition. Such investigations, which of necessity cover a limited field, give a reliable picture of the behaviour or response of the fungi concerned expressed in some arbitrary but standard terms such as dry weight. The results are of value because they can serve as the basis for systematic comparisons under fixed and reproducible conditions of growth and for metabolic investigations which are becoming of increasing importance in the study of fungal physiology, and they also have an industrial application. As early as 1922, Young & Bennett, using Mamosporium sarcineforrne, Fusarium oxysporum and Phoma apicola with the salts calcium nitrate, acid potassium phosphate and magnesium sulphate a t different molar concentrations, found that a correct balance of the mineral elements was essential for maximum growth, but that this behaviour varied according to the species of fungus used as test organism. Other workers have also obtained results indicative of a similar conclusion, until Talley & Blank (1941) gave the results of their careful statistical analysis of the nutritional requirements of Phymatotrichum omniworum, the causal organism of the root rot disease of cotton and other plants. These results showed that the absolute amount of certain essential metabolites was not so important as the balance between them. While the balance of salts may affect the overall metabolism of the fungus there are also indications that it may affect the synthesis of individual compounds such as penicillin. For instance, Pratt (1945) found that variations in the concentrations of KH,PO, ,