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 uncoloured 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. 
