MODELS OF BASIDIA 521 



Hiebert ; and the model of the Hymenom^-cete, made of brass 

 (top of basidhmi-body, sterigmata) and wood (stand, shaft of the 

 basidium-body, spores), was constructed by Mr. Churchward at the 

 University of Birmingham. The brass in the latter model was used 

 instead of wood to prevent the slender sterigmata from breaking 

 during demonstrations, transportation, etc. 



With the Rust model, to show how the basidium develops, one 

 first exhibits the teleutospore by itself, then adds to it the basidium- 

 body and its four sterigmata, and then the four spores. Similarly, 

 to show development with the hymenomycetous model, one first 

 exhibits the basidium-body with its four naked sterigmata and then 

 adds the spores. 



In the Rust model each spore has a slight hilum at its base. 

 This is where a drop of water should be excreted before discharge. 

 If one takes a little ball — such as a ping-pong ball — and holds it at 

 a hilum, one can indicate the position, general appearance, and size 

 of the water-drop. In the hymenomycetous model, unfortunately, 

 the spore-hila were not constructed. 



To illustrate the phenomenon of spore-discharge in still air with 

 the Rust model, one lifts the model from its stand, grasps the stalk 

 of the teleutospore in the left hand, and holds the main axis of the 

 model in a horizontal position. With the thumb and first finger of 

 the right hand one then takes hold of one of the spores and, keeping 

 hold of the spore, one makes it travel as rapidly as possible straight 

 outwards from its sterigma (more or less horizontally) for a distance 

 of about two feet, then turns it downwards sharply through a right 

 angle, and finally makes it descend vertically downwards with a 

 relatively slow terminal velocity without any acceleration. One 

 then deals with the other three spores in exactly the same manner. 

 At the end of these operations, the sterigmata are all vacant of 

 spores and one has made the audience clearly visualise the violent 

 mode of spore-discharge and the peculiar nature of the sporabolic 

 trajectory. One then handles the hymenomycetous model in the 

 same manner as the Rust model, and it at once becomes obvious 

 that the phenomenon of violent spore-discharge in the Uredineae 

 and in the Hymenomycetes is essentially similar. 



