96 RESEARCHES ON FUNGI 



the same time on any unit area of the hymenium probably decreases 

 with the gradual exhaustion of the hymenium, as was observed in 

 Panaeolus campanulatus and certain other Hymenomycetes. 



Marasmius oreades. — This fungus (Fig. 40), often called the 

 Fairy-Ring Fungus, is very common in Europe on grassy meadows 

 and lawns where it forms the well-known " fairy rings." Like 

 other Marasmii, it is able to withstand desiccation for some days 

 or weeks without loss of vitality. After a drought, when rain has 

 come, it quickly absorbs water through the surface of its pileus 

 and within a few hours begins once more to shed a cloud of spores. 

 In the general structure of the fruit-body as a whole, in its per- 

 sistence, and in the arrangement of the basidia in the hymenium 

 Marasmius oreades is organised in perfect accordance with the 

 Armillaria Sub-type. 



For our present purpose it is only necessary to describe the 

 appearance of the spores of the spore-bearing basidia of the hymen- 

 ium when this is seen in face view, for this gives the clue to the 

 arrangement of the basidia as a whole in respect to one another 

 both in space and time. A surface view of a piece of living hymen- 

 ium actively producing and discharging spores is shown in Fig. 41. 

 It will be seen at a glance that the arrangement of the spore-bearing 

 basidia is like that described for Armillaria mellea. The basidia 

 with the most rudimentary spores are well separated from one 

 another and not compactly arranged in groups. The same is true 

 of the basidia which bear full-sized spores, and of those which bear 

 spores of an intermediate size. The rule of wide separation of 

 basidia bearing spores of about equal age is well kept from day to 

 day throughout the whole period of spore-discharge. 



Russula ochroleuca. — Another excellent example of an Agaric 

 exhibiting the loose type of hymenium characteristic of the 

 Armillaria Sub-type is provided by Russula ochroleuca, a species of 

 which specimens were collected in the Midlands of England. In 

 order to bring out the rule, here again exhibited, that basidia bear- 

 ing spores about equally advanced in development are distantly 

 separated from one another and not packed together in little groups, 

 let us regard the spores in the accompanying illustration of a surface 

 view of the hymenium (Fig. 42) as roughly of four different ages : 



