6 DIVISION I.—GENERAL MORPHOLOGY, 
are much expanded or are in the act of expanding, which are little if at all 
thicker than the primary hyphae and are rich in protoplasm, and therefore look 
as though they were of recent formation. Whether they are really new branches, 
or only branches formed at an early period but not sharing in the expansion, 
must remain undecided. In the hymenium certainly new elements are introduced 
between the earlier ones usually for some time after its first formation. 
A distinct efinasty prevails at first in the general growth of the pileus; the 
parts belonging to the upper side grow more vigorously than those of the lower, 
and according to the position and breadth of the annular zone which is most strongly 
epinastic, either the margin of the pileus is rolled inwards or the whole of the 
under or hymenial surface approaches or even touches the stipe; or both effects 
are produced, and this is most frequently the case. Subsequently, when growth is 
coming to an end, the epinasty changes to Aydonasty, the under side grows more 
strongly than the upper, and the entire pileus expands with more or less rapidity 
in each separate case from its original bell-like or conical form into that of an 
umbrella, while the incurved margin may even become curved upwards and outwards. 
We cannot enter here into the variations which occur inthe development and form of 
the pileus in the several groups and species, and indeed we possess a very limited 
number of exact observations on them. The account which has just been given is 
founded on my own examination of Agaricus (Mycena) vulgaris, Pers., A. (Collybia) 
dryophilus, Bull, and Nyctalis parasitica, Fr., on the study of the history of 
development of Agaricus (Clytocybe) cyathiformis and Cantharellus infundibuli- 
formis in conjunction with Woronin, and on the works of H. Hoffmann. Hoffmann 
indeed makes the hyphae of the middle of the pileus in the section Mycena not 
run radially towards the surface and there terminate, but parallel to the surface 
of the pileus (for so I understand his expression ‘ horizontal’); and in this small point 
our otherwise conformable accounts differ. It is possible that different species vary in 
this respect. The course of the hyphae can be readily seen to be as I have stated it in 
Agaricus vulgaris, when the pileus is still young, but not in the older states ; then the 
whole of the superficial tissue of the pileus assumes the character of a tough gelatinous 
felt, which may be removed as a coherent membrane from the pileus, and in which the 
hyphae have no particular arrangement. 
In most of the sporophores of which we are here speaking, especially those of a 
fleshy consistence, growth proceeds without interruption and soon reaches its ter- 
mination; it may go on more slowly or be arrested for a time, if the conditions are 
unfavourable, and afterwards recommence ; more serious injuries, especially persistent 
drought and cold, stop it altogether. The power of withstanding such unfavourable 
influences varies much in the different species. On the other hand, as has been 
already stated, the pileus in many leathery and woody forms, such as the Xylarieae 
and especially the Hymenomycetes, has the power of recommencing suspehded growth 
with the return of favourable conditions. During each stationary period in the 
Hymenomycetes the hyphal extremities in the margin and upper surface of the 
sporophore, which for the most part die off, assume in many cases another colour and 
usually a darker one than that of the rest of the tissue, which is seen therefore 
in sections to be divided by dark lines into the zones already mentioned (Fig. 23). 
The tissue of the sterile surface also has often a different colour at the beginning 
from that which it has at the end of a period of growth ; and at the commencement of the 
period of growth it often swells suddenly into a cushion, which runs quite round the margin 
of the pileus and flattens out again towards the margin with the continuation of growth. 
The periods of rest and growth are thus here as elsewhere indicated on the sterile 
surface of the Fungus, as in some other plants, by zones concentric with the 
margin of the pileus, and usually answer exactly to the interior zones but are sometimes 
less distinctly marked. It is scarcely necessary to mention examples of these ‘ pilei 
zonati,’ since they occur in many of the most common and best-known species, 
