Refractometry of fungi

Immersion refractometry is based on matching the refractive index of the medium to that of the cytoplasm of the cell, in which case the latter will have minimum contrast in the phase contrast microscope and will practically disappear. The cytoplasm is then said to be at the match point with the medium. Since the refractive index of a solution is related to its concentration by the formula n-no equal alpha C, the values for the refractive indices can be expressed in terms of the concentration of solids (g/100 ml) which in fact has been done throughout this work. The properties of a suitable immersion medium, its preparation and interpretation of numerical results have been discussed. Refractometric measurements were carried out on fungal hyphae and spores. The solid concentration in hyphae varies according to their age, physiological state and function. In general the highest values are found at sites of physiological activity, such as growth and reproduction, and may range from 11% to 30% of solid concentration. The solid concentration of mature, resting spores was found to be in the range of 45-54%, with the exception of a powdery mildew spores in which the concentration of solids was 30-32%. The germination of spores is preceded by a fall in the concentration of solids, and subsequent swelling before the emergence of the germ tube. When the solid concentration in pre-germinating spore has fallen to about 20-30%, metabolic activity can take place and germination can occur.