Alternative fruiting pathways in phycomyces.
Developmental distinctions between giant and dwarf fruiting bodies of Phycomyces blakesleeanus (Burgeff) were studied by means of size measurements and growth analyses. Histograms of fruiting body lengths showed a bimodal distribution, with peaks around 0.3 millimeter (dwarfs) and 30 millimeters (giants). Individual cultures contain both giants and dwarfs. Differences between giants and dwarfs appear in the first phase of development; the apex of the giant is tapered, whereas the dwarf apex is dome-shaped. Probable cytological distinctions at this stage are cited in discussion. The dwarfs terminate enlargement upon expansion of the sporangium, thus lacking the subsequent phase of rapid elongation (stage IV) that contributes 90% of the length in the case of giants. It was concluded that P. blakesleeanus maintains two developmental patterns for asexual fruiting, with dwarfs and giants differing radically in growth regulation.
GROWTH OF PHYCOMYCES BLAKESLEEANUS IN RELATION TO VARIED ENVIRONMENTAL CONDITIONS
IN RECENT years the fungus Phycomyces Blakesleeanus Bgf. has been employed in physiological studies on a great variety of fundamental phenomena, such as light reactions, cell wall extension( see Castle, 1935, 1938), influence of vitamin B1 and other regulating substances (Burgeff, 1934; Schopfer, 1934, 1937, Bonner et al., 1939, Robbins, 1939), nutritional requirements (Leonian and Lilly, 1940), etc. The great sensitivity of this organism to physical and chemical stimuli makes it favorable for physiological studies and at the same time imposes the necessity for very careful control of experimental conditions. In connection with the use of the Phycomyces assay method for determinations of thiamin (B1) in higher green plants, marked differences in growth of the fungus were observed in relation to varied temperature, pH, organic content of the nutrient medium, etc. The purpose of this paper is to set forth certain of the experimental results obtained with cultures grown under various controlled conditions. Some of these data are of particular interest in relation to the use of Phycomyces as a biological indicator in assays for thiamin. A forthcoming paper will deal further with the latter subject. METHODS.-Unless otherwise stated, cultures were grown on 25 cc. of nutrient solution in Pyrex Erlenmeyer flasks of 125 cc. capacity. The basal medium contained the following dissolved in 1 liter of Pyrex distilled water: KH2PO4, 1.5 g.; MgSO4 7H20, 0.5 g.; and the trace elements (added from stock solutions of Fe2 (SO4)3, ZnSO4, CuSO4, MnSO4, H3BO3, and (NH4)2 MoO4)Fe, 0.05 mg.; Zn 0.10 mg.; Cu, 0.02 mg.; Mn, 0.01 mg.; B, 0.01 mg.; Mo, 0.016 mg. Because of traces of impurities in the salts, it is probable that the total concentrations of some of these elements may have been somewhat greater than indicated. In this medium there was included the amount and kind of nitrogen and carbon source selected for a particular experiment. The thiamin hydrochloride supplied to cultures was obtained from Merck and Co. All flasks of nutrient media were sterilized in an autoclave at fifteen pounds pressure for twenty minutes. Spores for inoculation were obtained from pure cultures of the fungus maintained on nutrient agar composed of the above basal solution plus 40 g./l. of glucose, 4 g./l. of asparagine, 20 g./l. of agar, and 10-6 M thiamin. A uniform suspension of spores was made for each separate experiment by shaking a quantitv of fresh mature sporangia in basal mineral solution. About one-tenth of a cc. of spore suspension was used
Investigations on the rôle of organic matter in plant nutrition
1. As the result of decomposition of green manure in a swamp soil, the coarse fractions (including coarse and fine sand) of the surface layer (first 3 inches) decreased by 11·2 per cent. while the fine ones (silt+clay) increased by 9·8 per cent. in the course of 43 days. The effect was less pronounced in the manured soil maintained at 60 per cent. saturation, while no alteration was to be noticed in the case of the unmanured specimens. 2. Treatment with dilute hydrochloric acid prior to dispersion had no appreciable effect on the estimates of mechanical composition obtained in the different cases. Loss in solution was also comparatively small. 3. The silica-sesquioxide ratio increased slightly as the result of decomposition of green manure in swamp soil. The composition of the fine fractions was also altered, the total percentages of the oxides of iron, aluminium and silicon increasing from 90·5 to 99·3 in the course of 71 days. 4. The practical significance of the above and related observations has been discussed.