142 RESEARCHES ON FUNGI 



gill do increase somewhat in area ; but this increase is due merely 

 to the increase in size of the individual basidia and paraphyses and 

 not to their multiplication. After the expansion of the pileus, the 

 hymenial layers on each gill remain quite constant in area until 

 the end of the spore-discharge period, i.e. until they have used up 

 their basidia in spore-formation and spore-discharge. The gills of 

 a Mushroom, after the expansion of the pileus, do not grow in depth 

 and therefore do not add to themselves progressively new r hymenial 

 areas. The result is that all the square millimetres of the hymenial 

 layers of a Mushroom begin and end their spore-discharge period at 

 about the same time. 



In Fomes applanatus, on the other hand, the hymenial tubes 

 are not developed throughout their whole length from the first, but 

 elongate slowly for many iveeks or even months. The cavities of the 

 tubes, when first formed, are merely hemispherical in shape. The 

 coalescent rims of these cavities then simultaneously all grow 

 vertically downwards, so that the cavities soon become shaped like 

 those of inverted cups and, finally, like those of inverted test- 

 tubes. White observed that, by the time the tubes had become 

 about 1'5 mm. (" 1/16 inch ") long in the first or second week 

 of May, the fall of spores had begun. 1 This indicates that the 

 hymenium lining the inner surfaces of the tubes is developed, just 

 as in Polyporus squamosus,* pari passu with the growth in length 

 of the tubes. By the end of July, White found that the tubes had 

 become 9'4 mm. long (" 3/8 inch ") and that after this time their 

 growth in length " slowed down considerably, gradually becoming 

 imperceptible." 3 We thus have direct evidence that the tubes 

 grow in length for the major part of the six-month spore-discharge 

 period. As the tubes grow in length at their pored ends only, 

 they progressively add new areas to the hymenium ; and, doubt- 

 less, each new area so added takes several weeks to exhaust its 

 basidia and shed all its spores. It seems to me, therefore, that the 



1 J. H. White, loc. cit., p. 139. * Vol. i, 1909, p. 92. 



3 J. H. White, loc. cit., p. 139. White, unfortunately, does not record the 

 final length of the tubes in October. It is to be hoped that someone will deter- 

 mine the rate of growth per week of the hymenial tubes of Fomes applanatus, 

 F. igniarius, F. fomentarius, etc., and present to us the results of his work in the 

 form of graphs. 



