28 DIVISION I. — GENERAL MORPHOLOGY. 



section VIII. The clews assumed a pseudo-parenchymatous structure owing to the 

 swelling of the cells of the hyphae, and the greater part of their surface acquired a brown 

 colour. Then one or several growing points appeared on most of the clews, always at 

 isolated uncolourcd spots in the part which did not project above the nutrient solution, 

 and from these points mycelial strands were developed of the subterranean form 

 just described. The primary mycelial hypha ceases to grow when the formation of 

 strands commences ; the strands also cease to grow as soon as the supply of nutri- 

 ment is exhausted. When cultivated on bread or with a larger supply of the 

 nutrient solution they developed vigorously and branched copiously, and showed all 

 the important points of the subcortical form described above. They remained 

 uncoloured beneath the substratum, and cessation of growth in length was followed 

 by specially copious development of gelatinous hyphae spreading from the surface, 

 and forming on the top of the fluid thick membrane-like patches of wefted covering 

 with a vesicular pseudo-parenchymatous structure, and with the cell-walls coloured 

 brown where they were in contact with the air. After a winter rest of several months' 

 duration a large number of strands of the subterranean form were again produced 

 from the cultivated specimens, being fed by them, and they were seen to make their 

 way into the roots of living pines, where their further subcortical development 

 was also observed. 



The development of the sporophores, which will be described in Division II, 

 begins according to Hartig on strands of both kinds in the same manner as the formation 

 already described of similar branches on the strands. 



Further details and variations, the great abundance of which is not to be wondered 

 at, considering the great variety of form and adaptation displayed by the strands of 

 Agaricus melleus, are to be found in the works of Hartig and Brefeld which are 

 cited further on. I have endeavoured to correct my own former statements, and some 

 also of those writers themselves, from these researches and some more recent ones 

 of my own. Some statements have not been satisfactorily explained even by these 

 investigations ; among them a former remark of mine in the first edition of this book, 

 that old and strong specimens of the subterranean form 'have often an uneven and 

 wrinkled rind, in which through subsequent luxuriance of growth the number of the 

 cell-layers is considerably increased and their arrangement is disturbed. I often 

 but not always found inside these specimens a brown zone concentric with the rind 

 from which it is divided by a narrow layer of ordinary medullary tissue, and enclosing 

 a strand of the latter tissue. This zone consists of hyphae with brown membranes 

 very tightly interwoven with one another, but in other respects resembling the ordinary 

 elements of the medulla, into which it passes without a break. Eschweiler's account 

 of the structure of the Rhizomorphae is founded on the examination of such specimens.' 



Future investigations will perhaps clear up these less important points. Greater 

 interest attaches to the question, whether the first development of the mycelium 

 observed by Brefeld, and especially the primary formation of the subterranean strand, 

 is an invariable occurrence in Agaricus melleus, or whether perhaps the subcortical 

 formations do not proceed directly from the mycelial hyphae, when the spores 

 germinate on a substratum which renders parasitic growth possible, that is upon 

 the living root of a conifer. 



The history of our knowledge of the mycelium of Agaricus melleus is somewhat 

 remarkable. Before R. Hartig discovered that the strands belonged to this Hyme- 

 nomycete, they were supposed to represent a distinct species of Fungus which was 

 named by Roth Rhizomorpha fragilis, or the two forms, the subterranean and the 

 subcortical, were made two distinct species, Rhizomorpha subterranea and Rh. 



