lO HUMPHREY 



consideration. In Monoclea the fungus is confined to a sharply 

 defined mycorrhizal zone three or four cell layers in thickness. 

 Many of the cells in this zone are filled with branched hyphae, 

 tufts of which seem to envelop the nucleus. In some cases 

 even the chromatophores, like the nucleus, become surrounded 

 by similar tufts of branching hyphai in a manner quite sug- 

 gesting the formation of a lichen. 



In Fossomhronia the hyphse preceding the development of a 

 sclerotium are but sparsely ramified. The first indication of the 

 sclerotium is the increase in diameter of the hyphas within a cell 

 followed later by the profuse development of short, thick 

 anastomosing branches between which may at first be seen 

 spaces of varying size which ultimately disappear as the 

 sclerotium increases in extent (Fig. lo). The nucleus and 

 chromatophores at first visible finally disappear, doubtless being 

 taken up by the actively growing fungus. As yet the writer 

 has failed to observe how these structures are consumed. 



According to Czapek ^ the tissues of Marchantia, Fegatella^ 

 Luniilaria and other hepaticae contain an antiseptic principle 

 which he calls " sphagnol " because of its abundance in the 

 peat-mosses. He has shown that this substance exists in com- 

 bination with the cellulose of the cell-walls and exerts an 

 inhibitive influence upon the development of moulds and 

 bacteria. This, Cavers ^ thinks, suggests the view that in the 

 case of certain Fusarium-like fungi the " sphagnol " may serve 

 to regulate the growth of the fungus and prevent symbiosis 

 from passing into parasitism. In the case of Fossonib^'onia it 

 cannot be shown that at any time during a period of infection the 

 invading fungus maintains a symbiotic relation with reference 

 to the host, for an examination of infected cells shows that the 

 presence of hyphas sets up a disturbance of the cell-metabolism, 

 the cell becoming impaired to such an extent as ultimately to 

 cause its death. The degree of this impairment varies with 

 the activity and extent of the parasite. To be sure, many 

 infected plants appear to be quite as healthy and fertile as 



'Czapek, 1SS9: Zur Chemie der Zell membranen bei den Laub. und Leber- 

 moosen. Flora, Band 86, p. 361. 

 ^Loc. cit., p. 33. 



