INJURIES INDUCED BY PLANTS 43 



Then, again, the mycelium frequently assumes the form of 

 branching strands, which enable the fungus to traverse strata 

 containing little if any nutriment. In such a case the strands 

 are either formed by the loose union of similar hyphae, when 

 they are called Rhizoctonice, or they are peculiarly constructed of 

 various kinds of organs. The strands of the dry-rot fungus 

 M. lacrymans, for instance possess, first, organs with wide 

 lumina and perforated transverse walls which resemble vessels ; 

 secondly, thin sclerenchymatous filaments ; and, thirdly, delicate 

 hyphae rich in protoplasm, and provided with clamp-cells. In 

 addition to such strands we have the so-called Rhizomorphs, 

 which, externally, present a close resemblance to the fibrous 

 roots of higher plants, while their internal structure displays 

 peculiarities which depend entirely upon the species of fungus 

 to which they belong. The best known of these are the 

 rhizomorphs of Agaricus melleus, which, when they have room to 

 develop, assume a round shape. In the cortical tissues of living 

 trees they spread out in a fan-like manner. Their internal 

 structure shows characteristic features, by which they may at 

 once be distinguished from the rhizomorphs of other fungi, e.g. 

 Dematophora necatrix. 



Functions similar to those of the tubers and rhizomes 

 of higher plants are to be ascribed to the so-called sclerotia. 

 These are peculiarly constructed masses of mycelium, in which 

 rich stores of nutriment, especially protoplasm and oil, are 

 deposited. After remaining quiescent, it may be for a long 

 time, they germinate on the recurrence of favourable conditions, 

 and produce either a new filamentous mycelium or the 

 sporophore of the special fungus. 



The simplest form of such resting-myeelia is represented 

 by the cell-groups of Cercospora acerina. Then come the 

 sclerotia of Rosellinia quercina, and the well-known sclerotia of 

 Claviceps purpurea* 



The sporophores which spring from the mycelium bear the 

 organs of reproduction that is to say, the spores which give rise 

 to new individuals. The same species of fungus frequently 

 produces different kinds of reproductive organs, which develop 



* [Rhizomorphs are also, in a sense, extended Sclerotia see also pp. 40 

 and 41. ED.] 



