THE EXTENT OF THE HYMENIUM 



33 



layers of tubes had been produced, and these possessed a total 

 vertical length of 40 mm. Hence, taking the three years together, 

 the total specific increase amounted to 493. 



Fomes igniarius. — In this species also, the fruit-bodies are per- 

 ennial and produce successive layers of tubes. In a large specimen 

 it was found for one layer that in 1 sq. cm. the number of tubes 

 was 2000. The breadth of each tube on the average was 0-15 mm. 

 and the length 4 mm. Hence, the area of hymenium for each 



(22 \ 



— X 0-15 j X 2000 = 3800 mm.^ approximately. 



Therefore, for 1 cm. 2, =100 mm.-, the specific increase = — =38 



^ 100 



approximately. In the specimen examined there were twenty-five 



Fig. 7. — View of part of a transverse section through the middle of a mature 

 fruit-body of Polyporus squamosus. The hymenial tubes are directed down- 

 wards. Natural size. 



layers of tubes, having a total thickness of 100 mm. For the total 

 period of growth, therefore, the specific increase amounted to the 

 high value of 942. 



From the figures just given, which show that in one year's 

 growth the specific increase for a specimen of Fomes ignarius was 

 approximately 38, and for one of F. vegetus approximately 148, 

 it is clear that the perennial Polyporese with narrow tubes produce 

 much more hymenial surface for a given area of pileus than any of 

 the AgaricineaB. The specific increase for Psalliota campestris, which 

 was the highest in the Agaricineaj investigated, was only 20-04. 



