A Rhizoctonia causing root disease in Uganda. W. Small. 159 



on the surface of the medium as small, whitish tufts. After a 

 day or two, the hyphae measure up to 8 ju. in diameter. Clamp 

 connections are found on the hyphae when they are a few days 

 old (Plate V, fig. 10), but never on the youngest threads. 

 Plate VI. fig. II shows the characteristic branching of 24 hours- 

 old mycehum in which the new branches pursue a course almost 

 parallel to the parent hyphae. The mycelium becomes granular 

 and de\-elops barrel-shaped cells \\ith oil-globules in 48 hours 

 (Plate VI, fig. 12). In three days the cells measure up to 30 ju, 

 in length, are granular and contain numerous oil-droplets, while 

 in eight days the mycehum presents the appearance shown 

 in Plate Vl, fig. 13. ]\Iany of the cells are then swollen and thin- 

 walled (Plate VI, fig. 14), while others are assuming the typical 

 Rhizoctonia outhne. In several cultures, especisJly in those 

 derived from fragments of sclerotial plate tissue, the mycehum 

 aggregates itself into dark strands which seem capable of be- 

 coming creeping rhizomorphs. The curious cell-formations shown 

 in Plate VI, fig. 15 occur in gro\\th from sclerotial plate and 

 h^Tnenophore fragments after a period of eight days. They are 

 most distinctly seen in filter-paper cultures. The majority of 

 them are terminal in position, and they frequently arise from 

 smaU thin hyphae. The rounded swollen cells are dark-bro\^Tl 

 in colour and well supplied \rith oil-droplets, and the general 

 formation of the mass of cells is irregular. The figure shows 

 several cells in process of segmenting and also the rounding-off 

 that follows di\-ision. Indi\'idually the cells resemble chlamydo- 

 spores, and, in the mass, the first stages in the formation of 

 sclerotia. Similar rounded dark cells occur singly or in small 

 groups in the course of the mycelium of certain cultures, but 

 neither their history nor that of the larger cell-formations has 

 been followed further. They presmnably perform a resting 

 function, for indi\'idual cells of the larger ty^Q can be found 

 separated from the general mass when the medium dries up. 

 When a filter-paper culture is allowed to drv and the growth 

 of the fungus is arrested in consequence, chlamvdospores are 

 formed in large numbers and at times so abundantly in the 

 course of the hyphae as almost to jostle each other for room. 

 They measure up to 8-10 ^ in diameter, and are thick-walled, 

 oily, and darker in colour than the hyphae. They are both 

 terminal and intercalary, and rounded or subpyriform (Plate VI, 

 fig. 16). A few of the darker cells have been noted in a state 

 of di\dsion, and it is probable that they would have given rise 

 to the curious ceU-masses mentioned above had development 

 been allowed to proceed. Besides the normal chlamydospores, 

 others which difter only in their reduced size can be found in 

 small groups as if budded off from the larger spores. They are 



