522 SCIENCE PROGRESS 



their path. The spores can then be seen falling in the form of curls and wreaths 

 of bright points. By this means the path of the spores could be followed and the 

 effect upon them of convection currents in the air could be studied. By this method 

 also the surprising discovery was made that forms such as the corky and leathery 

 Polypori and the xerophytic Marasmius and Schizophyllum will retain their vitality 

 for months or years in the dried state. They only require to be moistened for the 

 fall of spores, which is stopped by desiccation, to start again. 



The question of the manner in which the spores leave the basidia and escape 

 from the pores or from between the gills was closely investigated, and by dint of 

 careful observation and experiment the actual path of the spore was clearly shown. 

 The spores were found to be forcibly shot away from the basidia (not simultaneously 

 as stated by Brefeld, but successively) to a distance o'l to ot. mm. The mechanism 

 of spore-discharge is probably that of a jerk due to the sudden separation of the 

 two parts of a double wall in the sterigma. Such a wall was not observed, but since 

 the spore and basidium both remain turgid after separation a double wall must be 

 hypothesised. The specific gravity, size, and rate of fall of the spores in still air 

 were all carefully determined by ingenious experiments. From these data it was 

 calculated that the spore of Ainanitopsis vagi'nata leaves the basidium with a 

 horizontal velocity of about 40 cm. per second, and completes its horizontal path in 

 loo of a second. Later it falls vertically between the gills at a rate of about o'5 cm. 

 per second, which for some unexplained reason is about 46 per cent, more than would 

 be expected from Stokes' Law. 



As the spores of all the Hymenomycetes are very adhesive, a violent discharge 

 to a distance less than that separating opposite pairs of gills (or opposite walls of 

 a pore) is the only way by which spores can be provided with a means of free 

 escape from the hymenium of the ordinary fruit-body. The importance of the 

 vertical position of tubes or gills is thus made clear ; it can be calculated that in 

 the ordinary mushroom a tilt of about 5° will prevent the escape of half the spores. 



The function of the stipe is, as Falck suggested, the provision of a space beneath 

 the pileus within which the spores may be caught by air-currents. 



The author was unable to confirm Falck's theory of the importance of the 

 respiration of the fruit-body in producing heat and so giving rise to ascending 

 convection currents round the pileus. In the case of a fruit-body of Polyporus 

 squauiosiis examined tn the opoi the spores were seen to drift away sideways and 

 not to be caught up by vertical currents. It is possible, however, that such currents 

 may play a small part in other cases. 



The interesting problem of the advantage of the " deliquescence " of the gills 

 of the Coprini was attacked by the author. It is pointed out that the process is 

 probably one of autodigestion and that its purpose is apparently the removal of 

 parts of the gills which have already shed their spores ; by this means space is pro- 

 vided for the shedding of the next set of spores. Thus all the spores in succession 

 find a free path of fall, in spite of the fact that the frailty of the flesh of the pileus 

 prevents the gills as a whole being held horizontally as in the stouter fruit-body of 

 Agaricus. In the smaller, second part of his work Prof. Buller deals briefly with 

 the ejection and distribution of the spores in some Ascomycetes and in Pilobolus. 



In criticism it may be pointed out that although the author has succeeded in 

 giving for the first time a detailed working picture of the fruit-body of such well- 

 known forms as Agaricus, Polyporus and Coprinus, and so has earned the gratitude 

 of all botanists, yet he too readily assumes the absence of upwardly directed hymenia 

 in the group. Owing also to the slightly popular nature of the presentation of the 

 work the distinction between old and new material is not always clear. It may be 



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