THE HELVELLACE^E 



249 



The Helvellacese. — The Helvellacese are characterised by pos- 

 sessing long stipes which have exactly the same significance as 

 in the Hymenomycetes. The hymenium becomes raised up above 

 surrounding leaves and herbage, so that the spores, after being 

 discharged from the asci, can readily be carried off by air-currents. 

 A specimen of one of the largest 

 species — Morchella crassipes ■ — is 

 illustrated in Fig. 80. It was 9 

 inches high and therefore rivalled 

 in stature some of the largest of 

 the AgaricineaB. 



The pileus of a Morchella is 

 provided with anastomosing ribs 

 or plates which enclose irregular 

 polygonal pits. The hymenium 

 covers the whole of the exterior of 

 the pileus, so that it is evident that 

 the plates have the same function 

 as the gills of a Mushroom : they 

 serve to increase the amount of 

 the spore-bearing surface. How- 

 ever, if one compares the pileus of 

 a Morchella with that of a Mush- 

 room, one notices that the folding 

 of the hymenium is vastly more 

 compact in the latter than in the 

 former. The reason for this is to 

 be found in the fundamental differ- 

 ence between basidia and asci as 

 spore-liberating mechanisms. The 

 spores of a basidium are only shot 

 outwards to a distance of about 01 mm., whereas those of an 

 ascus are often propelled several centimetres. Hence adjacent 

 gill surfaces can be placed very near together without interfering 

 with the escape of the spores. On the other hand, the plates on 

 a Morchella pileus must be a considerable distance apart or the asci 

 would not have sufficient room for discharging their contents. 



Fig. 80. 



Fruit-body of Morchella cras- 

 sipes, an Ascomycete which resembles 

 many Hymenomycetes in having its 

 pileus supported on a long stipe. 

 Photographed at Winnipeg by C. W. 

 Lowe, i natural size. 



