l6 DIVISION I. — GENERAL MORPHOLOGY. 



to conduct air (Fig. 10). The spaces widen most in the centre of the axile strand ; in 

 the simplest case a single large axile cavity is formed, and narrow air-spaces join on 

 to it on the side of the periphery; in other cases single rows of cells remain in the 

 centre of the cavity separated for the most part from the adjacent tissue and therefore 

 quickly drying up; here too therefore there is really an air-filled axile cavity; its 

 diameter varies much, but it is always at least half as large as that of the strand, and 

 in strong specimens may reach a much larger relative size. 



The wall which encloses the cavity consists in its immediate vicinity of the 

 original large axile cells; these form about six irregular layers round the cavity, the 

 cells of the outer layers becoming gradually narrower, as was stated above, and it is 

 these layers which give rise to the medulla of the fully formed strand in the way which 

 will be described presently. Outside of the zone which produces the medulla are the 

 numerous layers of the close compact tissue, which ultimately forms the rind of the 

 strand. This tissue does not however extend to the surface ; this is occupied by a 

 supplementary stratum of about six layers of hyphae with narrow lumina and thick 

 gelatinous walls, which have coalesced into homogeneous mucilage, the gelatinous 

 felt mentioned above. The hyphae of this tissue run for the most part longitudinally, 

 and join with the hyphae of the apical tuft. They also give off spreading branches 

 from the surface. From these must be distinguished other spreading branches, also 

 provided with gelatinous walls, which spring from the hyphae of the rind beneath the 

 gelatinous felt, and pass transversely through it towards the outside. Their number 

 and distinction vary in individual specimens, and according to Hartig they are cf special 

 importance when the Fungus finds opportunity for adopting a parasitic life. A sharply 

 defined boundary line between the innermost elements of the gelatinous felted layer 

 and the outermost of the later rind cannot be drawn in the earlier stages of 

 development. 



The assumption by the tissue of its ultimate form begins with the thickening 

 and turning brown of the walls of the hyphae. It advances on the transverse 

 section from without inwards, and its first beginnings may be followed upwards 

 to the base of the young apical cone. As the coloration advances the gelatinous 

 felt which covers the rind dries up and usually no trace of it remains in older 

 strands. At the same time the formation of the ultimate medullary hyphae begins 

 'inside; these arise, as is shown in Fig, 12, as slender lateral branches from the 

 cells of the zone which produces the medulla, and from the innermost layers of 

 the rind which are not sharply distinguished from it ; these branches elongate 

 and ramify and enter the axile cavity, and becoming woven together there fill it 

 up in the manner which has been already described. As the zone which produces 

 the medulla always consists of several layers of cells, the hyphae which proceed 

 from its outer layers into the cavity must force their way between the inner layers, 

 which may become much displaced and squeezed together, ami this gives rise to 

 the irregularly constructed boundary zone between the medulla and the rind which 

 wa> mentioned above. A subterranean strand may form branches of the same 

 kind in varying number and with no regular arrangement. At the point where 

 a branch subsequently appears, a new formation in the form of a thick cushion 

 of pseudo-parenchyma is developed within the inner layers of the rind by shoots 

 from its cells, and the growing point of the strand emerges in a few days from 



