CHAPTER V. COMPARATIVE REVIEW. HYMEN OMYCETES. 



289 



the pileus, or come to an end on the surface of the pileus at different distances from 

 the insertion ; they may be shortly spoken of as lamellae of different and successive 

 orders. 



Each projection on the hymenium, lamella for example or spike, rises above 

 the hymenial surface, which in its earliest state is always level, in consequence of the 

 stronger growth perpendicular to the surface of the hyphae of which it is composed, 

 as compared with that of the portion of surface between the projections. Each 

 projection also when once begun grows perpendicularly to the surface and advances 

 towards the margin. This growth is quickly completed in the many short-lived 

 forms ; it may last for years in less transitory species with periodical alternations of 

 cessation and recommencement. See page 57. 



Attention has been already called at page 56 to the epinasty and hyponasty which 

 alternate according to the age, especially in rapidly growing forms with a pileus, to 



FIG. 132. Agariais campestrfs, L. a rthree stages of the development of a pileus in vertical radial longitu- 

 dinal section slightly magnified, a 6 mm., * 16 mm. in length. Successive stages of the development according to 

 the letters, d thin section of*, showing the course of the hyphae, enlarged and somewhat diagrammatically repre- 

 sented, r the veil (annulus). 



the consequent primary involution of the margin of the pileus or application of the 

 hymenial surface to the stipe, and lastly to the expansion of the pileus. 



Hymenomycetes with compound sporophores of purely marginal or apical 

 progressive growth are termed gymnocarpous, because the hymenium lies from 

 the first on the free surface and is not covered by any special envelope, though 

 it is protected when young by adjacent hairs and by epinastic curvatures. 



SECTION LXXXVI. Many Agaricineae and some Boleti differ in one respect 



from true gymnocarpous forms, since the growth of their stalked pileus or of a 



portion of it goes on within a special envelope, which was termed by Persoon 



the involucrum, by Fries the velum or veil; the latter name is still generally 



[4] 



