297 



chains, which are formed acropetally, it must be placed in the 

 section Oosporeae, and Miss E. M. Wakefield, "who examined my 

 cultures and material suggests that it would be most suitably 

 placed in the genus Oospora itself, and that it must be regarded 

 as an undescribed species. I am much indebted to her for 

 assistance with regard to its systematic position, and for the 

 following description : — 



Oospora pustulans, Owen 8f Wakef. sp. nov. 



Fungus filamentosus, sub epidermide pustulas minutas nigras 

 efficiens. Mycelium repens, delicatulum; hyphae septatae primo 

 hyalinae, 2-4 fx diametro, demum (in culiis) fuscae, torulosae, 

 ad o-7 (-10) fx diametro. Conidiopltora erecta, curta, a mycelio 

 baud distincta. Conidia cylindrica vel oblonga, hyalina, 

 6-12 x 2-2*5 jtx, aetate provecta intus vacuolata, ideoque spurie 

 1- septate, in catenas longas plus minusve ramosas digesta. 



Habitat: parasitic on tubers of Solanum tuberosum, forming 

 minute pustules on the surface. 



It should be noted that though the spore chains are sometimes 

 branched, the branching is quite indefinite and the conidia arise 

 directly from the hyphae without the intervention of a special 

 swollen basal cell, as occurs in the section Aspergilleae. In very 

 vigorous cultures the chain of spores are sometimes repeatedly 

 branched and spread out in a fan-like manner. 



The discovery of a fungus belonging to the genus Oospora at 

 • once recalls Thaxter's well-known Oospora scabies , the name long 

 given to the organism causing common potato scab. A detailed 

 account of this organism has been given by Lutman and 

 Cunningham (Vermont Agric. Expt. Station. Bull. 184, 1914), 

 where Thaxter's original description is quoted. It will at once be 

 seen that the present organism differs in the possession of much 

 larger hyphae and in the oblong spores borne in chains. Thaxter's 

 plant is in fact not an Oospora, and is now generally regarded as 

 belonging to the genus Actinomyces. 



Inoculation Experiments. 



All experiments dealing with the relation of Oospora pustulans 

 to its host are much handicapped by the slow development of the 

 fungus. The results of inoc illations made under field-conditions 

 in the early summer were not obtained till the following winter 

 or early spring, and it will be necessary to wait another season 

 before the results can be confirmed or amplified. 



Two laboratory experiments made with freshly dug tubers of 

 an early variety during June, 1918, may first be described. In 

 order to accelerate the development of the spots, tubers inoculated 

 with spores and placed on damp blotting paper in a large petri 

 dish were kept in an incubator at 22° C. Under these conditions, 

 however, the tubers did not remain normal. The lenticel tissues 

 grew out, and straggly shoots developed from the eyes. At the 

 end of three months there was no obvious sign of infection and 

 the tubers were placed in a dark cellar, being examined 

 periodically, with no results until early in April, when one or 

 two isolated spots were found. In the light of the previous tests, 



