CHAPTER V.—COMPARATIVE REVIEW.—HYMENOMFCETES. 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. Agaricus campestris, L. a—c three stages of the development of a pileus in vertical radial longitu- 
dinal section slightly magnified, 2 6 mm., 5 16 mm. in length. Successive stages of the development according to 
the letters. @ thin section of 4, showing the course of the hyphae, d and di: ically repre- 
sented, 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 veel; the latter name is still generally 
[4] u 
