R.A. Davey

Ballistospore discharge in Itersonilia perplexans

Ballistospore discharge in Itersonilia perplexans is described. Evidence is presented that a drop of liquid, and not a gas bubble, develops at the hilar appendix immediately before discharge. Spores detached on a micromanipulator needle produce liquid drops. The trajectories of several spores have been plotted. The horizontal and vertical distances of discharge have been measured, and the terminal velocity of sedimentation. From these values, the initial discharge velocity has been estimated at 5.5 m s−1. Evidence is presented that discharged spores carry a negative electrical charge. Two possible mechanisms for spore projection are discussed, a rapid transference of the centre of mass of the spore associated with wetting, and a change in the electrical charge on the spore surface at wetting, followed by electrostatic repulsion.

Sigmoid conidial shape in aquatic fungi

Observations on the orientation of sigmoid conidia of aquatic fungi during flow and on coming to rest have been made in flat capillary tubes. Conidia are arrested by attachment at one end, and then swing round so that they are aligned parallel to the direction of the current. After a short period of attachment ‘appressoria’ and germ tubes develop where the conidium makes contact with a surface. Experimental evidence suggests that there is a contact stimulus to germination.

Origin of the liquid in Buller's drop

The origin of the liquid in Bullers drop is discussed and evidence presented that Tilletiopsis washingtonensis and I. perplexans may extrude a hygroscopic substance from the punctum lacrymans , resulting in rapid absorption of liquid from a humid atmosphere.

Measurement of the electrical charge on some basidiospores and an assessment of two possible mechanisms of ballistospore propulsion

Estimates of the charge/mass ratio Q/m on ballistospores of several Basidiomycetes have been made by measuring the deflection of falling ballistospores when an electrostatic field is applied. There is a wide range of values within individual species. The mean value also varies over a wide range between the species studied, from 12.8 × 10−4 C kg−1 for Itersonilia perplexans to 0.3 × 10−4 C kg−1 for Agaricus bisporus. Various lines of evidence indicate that electrical forces can, at best, play only a minor role in the discharge process. A hypothesis based on surface tension appears to us to provide a more likely mechanism.

Dendrosporomyces prolifer gen. et sp.nov., a basidiomycete with branched conidia

A branched spore isolated from foam in the Gombak River, Selangor, has been grown in culture. The development of conidia, resembling the form genus Dendrospora , is described. However, light- and electron-microscope evidence shows that the fungus has dolipore septa, indicating that it is a member of the Basidiomycotina, whilst the type species of Dendrospora, D. erecta , has simple septa. The fungus is described as the type of a new genus Dendrosporomyces . A basidial state has not been observed.

Sedimentation rates and trapping efficiency of cells of Candida aquatica

Candida aquatica an aquatic yeast from hollow internodes of Equisetum was grown in culture under nutrient-rich and starvation conditions. Under nutrient-rich conditions the cells form short oval buds arranged to form a tetraradiate propagule, whilst starved cells form tetraradiate propagules with septate tapering arms. The sedimentation rate of ‘nutrient-rich’ propagules was up to 20 times greater than for ‘starved’ propagules. The trapping efficiency of ‘starved’ propagules was about twice as great as that of ‘nutrient-rich’ propagules. It is suggested that these properties are adaptively related to habitat.

A simple technique for demonstrating Buller's drop and ballistospore discharge from agaric gills

Basidiospore discharge can be demonstrated in gill sections laid on tap water agar. The enlargement of Bullers drop is not accompanied by diminution in the dimensions of the basidiospore from which it develops.