WITH NOTES ON OTHER SPECIES. 67 



SAPEOLEGOTACE^. 



The vegetative organs of these plants consist of nsuallj branched tubnlar fila- 

 ments without dividing walls, and therefore with a single continuous cavity. The 

 filaments are of two sorts — the internal threads, which penetrate the substratum, 

 branching freely, and tapering rapidly to their pointed ends (Fig. 2), and the external 

 ones, which arise from the latter and radiate outward into the surrounding medium 

 (Fig. 1). The following description refers chiefly to the latter. 



In general, there are no sudden changes in the calibre of a filament, but only a 

 gradual decrease from one end to the other ; but the Leptomitere are characterized by 

 abrupt constrictions at intervals, marking off the hyphse into segments, but not 

 completely closing the cavity (Fig. 6). The hyphae are usually largest at their 

 bases ; that is, where they arise from or give rise to threads of the other kind. 

 From this point the external threads decrease slowly in size. Those of Leptomitus, 

 however, decrease abruptly with each successive branching, so that their apical seg- 

 ments become reduced to an eighth of the diameter of the basal ones. The different 

 species present very wide extremes in the size of their filaments, whose diameter may 

 vary fi'om S;j. in Aphanomyces to more than 100,/ in 8. Treleaseana. The length of 

 the filaments in any given species or individual is considerabl}^ aftected by the 

 amount of available nourishment; but in vigorous specimens of ApJianomyces it 

 may not exceed two or three millimeters, while in some AcJilyce it may reach more 

 than twenty millimeters. 



The hyphal walls of the members of this family are composed, unlike those of 

 almost all other fungi, of unmodified cellulose, which reacts readily and charac- 

 teristically with chloroiodide of zinc. Within this wall is a layer of protoplasm which 

 lines it closely and forms a hollow cylinder. At the centre is a wide vacuolar space, 

 across which run, especially in the younger parts of the filament, strings of proto- 

 plasm connecting opposite parts of the parietal layer. This layer is densest and 

 most granular in the youngest or apical part of the filament, and in the older parts 

 the granular protoplasm forms a network of anastomosing threads or bands, with 

 somewhat wide interstices (Fig. 4). In the threads of this network a constant 

 circulation is kept up, towards the base in some and towards the apex of the hypha 

 in others. It is worthy of remark that when young threads are cut off in water their 

 death does not necessarily result. A^ery little protoplasm is lost from the tube thus 

 opened, but a new cellulose wall is very quickly formed across the cut end (Fig. 3), 

 and the hypha remains capable of normal development if nourishment be again sup- 



