Apr. 29. i9i8 Stemphylium Leaf spot of Cucumbers 299 



plants being kept under conditions more favorable for infection. In 

 this case infection occurred on all the inoculated plants, cucumbers, egg 

 and pear-shaped gourds, crookneck and White Bush Scalloped squashes 

 (PI. 23, A. B). These exepriments have been repeated in the field with 

 similar results. 



Repeated attempts have been made to obtain infection on other parts 

 of the host than the leaves. In the case of cucumbers only, an occasional 

 infection on stem and petiole has resulted when the plants were kept 

 continuously in the culture chamber. 



The various inoculation experiments have afforded abundant oppor- 

 tunity for observing the effect of age on the susceptibility of leaves to 

 infection. Infection may occur on the youngest unfolding leaves, but 

 is much more abundant on the older leaves. The spots develop more 

 normally on the older leaves, and spore formation occurs earlier and more 

 abundantly. 



Through the inoculation experiments outlined above, the parasitism 

 of this fungus to the leaves of cucumbers, and certain varieties of gourds 

 and squashes would seem to be clearly established. Successful inocula- 

 tions were made on the following four varieties of cucumbers : Arlington 

 White Spine, Nichol's Medium Green, Heinz Muscatine, and Davis 

 Perfect. 



TAXONOMY AND DESCRIPTION OF THE FUNGUS 



This fungus belongs in the family Dematiaceae of the Hyphomycetes. 

 The dark, muriform, subglobose conidia place it in the group Dictyo- 

 sporae. Careful consideration of the fungus, both in the field and in 

 artificial culture has led the writer to place it in the genus Stemphylium.^ 



The following is a brief description of the fungus : ^ 

 Stemphylium cucurbitacearum, n. sp. 



The fungus produces spots ranging from 0.2 to 15 mm. in diameter upon leaves, 

 rarely stems and petioles. The smaller spots vary from circular to angular in outline, 

 with a light yellowish brown center and a darker reddish brown border, rarely white, 

 on the upper surface; the spots are lighter on the lower surface. The larger spots 

 vary from white to light brown, with reddish brown areas along the veins, giving a 

 mottled appearance. 



The mycelium is hyalin to light brown, vacuolate, septate, branched, growing read- 

 ily on various culture media. Diameter, 2.5 to 10 ju. Fusion of the hyphse is quite 

 common. 



' A specimen of this fungus was submitted to Dr. W. G. Farlow who verified the writer's conclusions in 

 regard to its systematic position. 



- Stemphylium cucurbitacearum, sp. nov. — Maculis in foliis, raro caulibus. o.a to 13 mm. in diameter; 

 maculis tninoribus orbicularibus vel angularibus, ad superficiem ccntro pallido-luteo-brunneis, rufo- 

 brmmeo-marginatis raro albidis, infra albidis; maculis largioribus albidis vel laete-brunneis per venas 

 rufis-fuscis; mycelio hyalino vel laete-brunneis; septato, ramoso; sporophoris hyalinis vel laete-brunneis 

 1-5 septatis, 10-30 X 7-12 *», cellulis singulis deinde globosis; sporidiis muriformibus, subglobosis, atro 

 bnmneis 25-50 n diameter, e cellulis 5-20, 10-18 /i diameter, hypophyllis, in apice sporophororum singulis. 



Habitat in foliis vivis, raro caulis, Cucumeris sativi et Cucurbitae peponis, Plymouth, Lapaz, Lakeville, 

 Hamlet, et North Liberty, Indiana; et Bowling Green, Ohio, America Borealis. 



