EXPERIMENT STATION BULLETINS. 657 



found in this country. This must be recognized in all discussions of ex- 

 periments performed by European investigators with this fungus. 



Pending a comparison of the Septoria Leaf-spot from.Argentina, the 

 specific name "lycopersici" is used. 



RELATION OF FUNGUS TO HOST. 



Morbid Anatomy: 



The Spore on the Host: 



In order to follow the course of infection, inoculations were made on 

 a number of plants. The epidermis was stripped off from the inoculated 

 leaves at intervals of 6-12-24-36-48 hours. Examination showed germi- 

 nating spores; at the end of 48 hours these appeared similar to spores 

 in culture. (See p. 15), The great number of spores lengthened and 

 grew from both ends. This was soon followed by germ tubes arising 

 from various points on the spore. The type of infection is stomatal. 

 (See Plate 4, Fig. 2). The mycelium may immediately enter a stoma. 

 The spore in making its primary terminal growth in germination may 

 enter the stoma, or if the mycelium does not come in contact with stoma 

 immediately, the germ tube may branch and grow over the surface until 

 it strikes a stoma. No chemotactic action leading to the finding of the 

 stomata seemed to be manifested. 



Mycelium and Tissues: 



Infection may occur on both sides of the leaf. Careful study of the 

 two types of infection were made in the various experiments when in- 

 fection was desired. It was noted that when spores were placed on the 

 upper surface of the leaflet, infection was manifested in small, narrow 

 spots with from one to five pycnidia; the infection being more or less 

 confined to the midrib and veins of the leaflet. Infection produced by 

 placing the spores on the lower side of the leaflet resulted in a broad, 

 spreading spot, and resembled for the greater part, field infection of the 

 lower leaflets, spots forming at all points of the leaflet. This was veri- 

 fied by using one standard loop of spore suspension for inoculation on 

 the upper and lower surface of leaflet, respectively. 



Haustoria : 



Immediately on entering the stoma, knob-like haustoria developed 

 (See Plate 6, Fig. 2), These may be formed at once upon entering if 

 the mycelium touches the cell wall. By enzymic action, the haustorium 

 merely dissolves the cell wall, but does not penetrate deeply into the 

 cell. A gradual shrinking of the pierced cells results. The mycelium 

 grows luxuriantly through the leaf, making its greatest growth in the 

 spongy tissue. At the end of five days the tissue is partly disintegrated 

 and pycnidia begin to form. The mycelium commences to ball up and en- 

 large. 



The mycelium is not confined to the disintegrating tissue. It is found 

 in abundance through the tissue contiguous to the spot, in most cases 

 terminating at the tracheary cells. In this outside tissue the cell rela- 

 tions are similar to the cells at the point of initial infection after the 

 mycelium had grown for four days. 



The period from the fifth to the thirteenth day after inoculation is 

 characterized by the gradual shrinking and blackening of the tissues. 

 From the half-submerged pycnidia the spores ooze out. The white spore 

 83 



