170 RESEARCHES ON FUNGI 



position, stand somewhat nearer to the Uredineae than to the 

 non-tremelloid Hymenomycetes. This, perhaps, may be taken as 

 one more small piece of evidence that the Tremellineae and the 

 Uredineae are closely related. 



It has already been pointed out that, under natural conditions, 

 the whole or part of the hymenium of the most gelatinous fruit- 

 bodies of the Tremellineae (Tremella, Ulocolla, Exidia, Dacryomyces, 

 etc.) often looks more or less upivards. This upward-looking 

 position is very exceptional in the Hymenomycetes and calls for 

 some explanation in connection with the dispersal of the spores. 

 In most Hymenomycetes, e.g. Stereum, Polyporus, Psalliota, and 

 Hydnum, the hymenium is on the under surface of the pileus and 

 always looks more or less downwards. This enables the spores, 

 which are shot out from their sterigmata a distance of 1-0 2 mm., 

 to fall into a space beneath the pileus and to be carried off there- 

 from by air-currents. If the hymenium were to look upwards, 

 spores shot 0-1-0-2 mm. would be liable to fall back on the 

 hymenium and adhere there before the wind could carry them 

 off. The Discomycetes with upward-looking hymenia are successful 

 in dispersing their spores because the spores are usually shot 

 upwards from the asci for a distance not of 0-1-0-2 mm. but 

 of 1-3 cm., i.e. about one hundred times farther than for most 

 Hymenomycetes. This distance of discharge gives plenty of time 

 for the wind to carry off the spores before they can fall back again 

 on to the hymenium. 1 Now it is a remarkable fact that the 

 gelatinous Hymenomycetes in which the whole or part of the 

 hymenium looks more or less upwards discharge their spores 

 much more violently than non-gelatinous Hymenomycetes in 

 which the hymenium looks more or less downwards. It seems to 

 me, therefore, that the upward-looking position of the hymenium in 

 so many Tremellineae and the exceptional violence of spore-discharge 

 in that group are correlated. We may conclude that, from the 

 point of view of spore-dispersal, the disadvantage of the more or 

 less upward-looking position of the hymenium of many Tremel- 

 lineae, e.g. Exidia albida and Dacryomyces deliquescens, is com- 

 pensated by extra violence in the discharge of the spores. 

 1 Cf. vol. i, 1909, pp. 21-24. 



