PANAEOLUS CAMPANULATUS 313 



analogy that we should find this arrangement in existence. How- 

 ever, the rapid collapse of basidia which have shed their spores, 

 whatever its physiological cause, fits in very well with the general 

 organisation of the hymenium. It would be distinctly disadvan- 

 tageous for exhausted basidia to remain protuberant, owing 

 to the fact that their sterigmata, and any undischarged spores 

 which they might carry, would be liable to be in the way of the 

 new spores in course of development or discharge. By their rapid 

 collapse after shedding their spores, basidia get rid of their sterig- 

 mata entirely, and they also drag down any spores, which they 

 have not succeeded in discharging, to the general level of the 

 hymenium. After having been brought to this low level, these 

 wasted spores are mechanically harmless ; for, as we have seen, 

 maturing basidia, when elongating, push them aside without 

 difficulty. The rapid collapse of exhausted basidia is therefore 

 significant from the point of view of the organisation of the 

 hymenium as a whole, in that it leads to the rapid removal 

 of useless sterigmata and wasted, spores from positions where 

 they might form mechanical hindrances to the development and 

 discharge of the spores of later basidial generations. 



The Relative Position of the Basidia and the Spores of One 

 Generation. The distribution of the basidia belonging to a 

 single generation is shown for Panaeolus campanulatus in Figs. 89 

 (p. 257) and 90 (p. 258). It follows no precise mathematical 

 rule. However, one can see from inspection that the basidia are 

 separated from one another by such distances that their spores 

 cannot come into contact with one another : mutual interference 

 is rendered impossible. At the same time the basidia are sufficiently 

 evenly spread over the hymenium, and sufficiently near to one 

 another, to prevent there being any great waste of space. The 

 distances separating the basidia are usually confined within fairly 

 definite and circumscribed limits. If one considers the area shown 

 in Fig. 89 (p. 257), one sees that there are not many places where 

 one could insert additional spore-bearing basidia without reducing 

 to a dangerous minimum the margin of safety for securing the 

 isolation of the spores of each basidium. We may conclude that, 

 for Panaeolus campanulatus, the distribution of the basidia of any 



