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.
New photoresponses of phycomyces.
The influence of light on asexual fruiting and mycelial growth of Phycomyces blakesleeanus Burgeff was studied by means of fruiting body counts and size measurements in cultures on solid media under varied incubation conditions. Five types of photoresponses were shown by ATCC Strain 8743a: (a) photoinduction of giant sporangiophores; (b) interference by light with an endogenous system that otherwise induces fruiting when the mycelium approaches the rim of the Petri dish; (c) inhibition of mycelial growth rates by light; (d) inhibition of dwarf sporangiophore induction by light; and (e) postponement by light of death in clones maintained by serial transfer at low temperature. A second strain, designated G5, showed responses comparable to (a), (b), and (d). The magnitudes of the responses were greatly affected by temperature of incubation and available nitrogen (asparagine) supply. The photoinduction of giant sporangiophores could be demonstrated with light of wavelengths between 380 and 480 nanometers but not with 520 nanometers or above. At 480 nanometers, light doses as small as 40 ergs per square centimeter were effective in inducing giant sporangiophores in strain 8743a.
STUDIES ON THE NUTRITION OF FUNGI. IV. FACTORS INFLUENCING THE GROWTH OF SOME THIAMIN-REQUIRING FUNGI
THE NECESSITY of an extraneous supply of thiamin for the growth of many fungi has been definitely established, but we know comparatively little concerning the influence of a number of contributory factors upon the growth of such organisms. The present investigation is an attempt to extend our knowledge concerning these factors. Part I of this paper concerns itself with the agar factor; Part II with the effect of organic acids upon nitrogen utilization; and Part III with nitrogen-dextrose-thiamin ratio. TECHINIQUE.-Unless otherwise stated, all cultures were grown on 25 ml. of nutrient solution in Erlenmeyer flasks of 250 ml. capacity. The basic medium consisted of 0.5 gram each of ammonium nitrate, potassium dihydrogen phosphate, magnesium sulfate, 5 grams of Bacto-Dextrose of highest purity, 0.5 gram of a mixture of amino acids (d-arginine, d-glutamic acid, 1-aspartic acid, 2 parts each, and 1 part each of glycine and dl-a-alanine), Robbins and Kavanagh's (1938) modification of Hoagland's A-Z mixture of rare elements, and 1,000 ml. ,of distilled water. This solution, as well as all its modifications, was adjusted to pH 5.5 by means of sodium hydroxide. The amount of auxithals varied according to the nature of each experiment. The foregoing solution containing 1/100th ppm. thiamin was solidified by 2 per cent agar, and 15 ml. of it was poured in a series of 90 ml. Petri dishes. These were autoclaved and inoculated with the various test organisms to furnish the necessary stock cultures. All flasks were inoculated by means of inoculum discs cut from the vigorously growing Petri dish colonies by means of a cork borer with an opening of 5 mm. in diameter to insure inoculum pieces of uniform size and vigor. All cultures were made in quintuplicate and incubated at 25?C. for various lengths of time. The crop was then harvested, and five mycelial mats in each series were comI Received for publication October 16, 1939. Published with the approval of the Director of the West Virginia Agricultural Experiment Station as Scientific Paper No. 227. bined and dried at 100?C. to constant weight. Thus each figure given in the following tables, unless otherwise stated, represents the composite weight of five cultures. The actual weight of mycelium obtained under controlled conditions has been made the criterion for the evaluation of the comparative effectiveness of various factors. However, it should be emphasized that biological phenomena cannot be reduced to mathematical figures without making a generous allowance for the frequent and often disconcerting fluctuations that characterize the behavior of living things. No matter how rigidly one mav control the environmental conditions and repeat a given experiment, one will always find some differences in the weight of the crop. Even the different cultures of the same experiment made at the same time and under identical conditions will continue to vary. We have found that such variations may be from 5 to 10 per cent; however, this is not great enough to be significant.