IN spite of the fact that the shape of toadstools seems so peculiarly to suit the function of spore discharge it must not be too hastily assumed that this function brings about their shape. There are toadstools where the gills are such an impediment in the way of spore dispersal that the spores cannot be freed until the gills have dissolved. Even here the toadstool shape is still retained. It is at least a stimulus to the imagination to consider these structures in the light of pressure and stability. It is generally conceded that some of the structural lines in animal bones revealed by X-rays are developed in response to the direction of thrust, and in the same way in general terms it may be said that animal skeletons correspond structurally to bridges where girders are placed along the main pressure and tension lines. If a toadstool is growing against the pressure of the earth that pressure might be expected to develop corresponding structures in the same way as in animals, and if the form of a toadstool is considered as being a compound arrangement of cantilever brackets (cap and gills) set in a wall (the) the shape of the toadstool becomes intelligible on engineering principles.
The air-drift method is not the only manner in which fungus spores are distributed, though it is certainly the
main one. Invariably there is some kind of preliminary explosion, which may vary from the small one of a toadstool, to the larger one of a puff-ball, or of the sac-like bodies that comprise the fruit of one of the cup-fungi. These, although tiny, may in the mass explode with sufficient force to make a sharp hiss.
Occasionally, as with the well-known stink-horn, carrion-flies crawl over the surface and sticky spores adhere to their bodies. A commonon dung, called Pilolobus has an arrangement by which a ‘bullet ‘of spores can be shot off some six feet into the air after the ‘gun ‘has been carefully sighted towards the light. The spore-mass is sticky and adheres to grass, and if the grass is eaten by horses the cycle is completed. Another fungus called Sphcerobolus throws out a spore-mass in a similar fashion, but in this fungus the mechanism is not sensitive to light and the projectile is exploded from a mortar rather than from a gun. All kinds of ‘creepies and crawlies,’ mites, insects and slugs play a part in distributing fungus spores so universally as to make them, as they are, the common organisms of everyday life.
The efficiency of these methods of distribution does not seem to be high. Fungi seem to be prodigal in spore production, but few spores are favoured by destiny. It may reasonably be assumed always that the saturation point of any environment is quickly attained, and the maximum number of organisms develop that conditions will permit. The pressure of competition may drive useful scavengers into parasitism, or not, according to the material we provide and the control we exercise, so that to a large extent it may be said that the future of this group of organisms lies in man’s hands.