In addition to conventional measurements of colony radius
that are used to analyze the effect of temperature on growth,
we also determined the rate of increase in the volume of invasive hyphae (in units of mm3 h1). These measurements were
made in order to explore whether these data might reveal
more about the invasive behaviour of the three Pythium species (only strain 28251 of P. insidiosum was examined in the
growth experiments) that would be relevant to their growth
in the natural environment. The raw data for the volumetric
expansion estimates consisted of measurements of the radii
of the submerged portion of colonies (rather than the length
of the hyphae traveling over the agar surface) and measurements of hyphal diameter to the nearest 0.5 mm at a distance
of 100 mm from the cell apex. The diameter of 20 hyphae was
measured from pairs of Petri dish cultures (ten hyphae per
plate) incubated at temperature intervals of 5 C between
7 C and 37 C. For those species that continued to grow above
37 C, cultures were incubated at higher temperatures until
the complete cessation of growth was observed.