56 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 epinasty 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 hyponasly, 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 in the 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 suspended 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, 



