EXPERIMENT STATION BULLETINS. 583 



lumen and penetrate other cell walls as they are encountered. No cases of 

 penetration between cells, by wedging apart of cell walls or by dissolving the 

 cementing substances were discovered. A few cases of stomatal entrance 

 were noted but these were not numerous enough to denote any special at- 

 traction on the part of the stomata for the fungus. Those tubes which en- 

 tered in this manner probably did so by chance rather than as an easy method 

 of gaining entrance to the host tissue. As the fungus normally attacks the 

 underground parts where stomata are scarce or lacking, it is obvious that 

 methods of entrance must be confined to other natural openings, to wounds, 

 or to direct penetration. These observations estabhsh the fact that the fun- 

 gus is capable of making its own openings in the leaf -blade and petiole. The 

 same is doubtless true in the case of roots and crown. 



With young plants, 100 per cent infection is quite frequently obtained; 

 older plants, when inoculated, often fail to take the disease. This obser- 

 vation has been made repeatedly with greenhouse plants. Young seedlings 

 are subject to rapid infection. As the plants increase in age, indications of 

 extreme susceptibility become less marked, though age by no means renders 

 them immune. Full grown plants can be made to take the disease under 

 certain conditions. As the plants become older the tissues become tougher 

 and no doubt offer more resistance to invasions of this frnigus. Breaks in 

 the epidermis under these conditions would offer opportunity for the patho- 

 gen to gain a foothold. 



To determine the effect which w^ounding would have on the percentage 

 of infection in the case of older individuals, 50 plants were selected and 

 wounded in the region of the crown by scratching into the tissue with a 

 sharp needle. Bits of mycelium were placed in direct contact with these 

 breaks in the epidermis. At the same time, an equal number of checks was 

 inoculated by placing mycelium in contact with unbroken tissue. The 

 plants were kept under conditions favorable for the progress of the disease. 

 At the end of two months, 48 of the 50 wounded plants had developed black 

 rings around the crowTis, and a large number of roots had been lost. Of 

 the check plants, 32 of the total 50 showed typical signs of the disease, but 

 the invasions were more restricted and much less serious in their effect on 

 the normal functioning of the host plants. 



Under average conditions in the field, wounds due to insect bites, fungus 

 invasion, mechanical injuries, etc., are common. Such injuries in all proba- 

 bility are an aid in admitting the root rot fungus, but by far the greater percent- 

 age of infection probably takes place through the unbroken epidermis. Es- 

 pecially is this true in the case of young plants which may suffer a high per- 

 centage of infections. Older plants which offer more resistance to invas- 

 ions are no doubt less susceptible when they present an unbroken surface. 



PATHOLOGICAL HISTOLOGY. 



Previous investigation by Klebahn (5) has shown that the Phoma Root 

 Rot organism grows both intercellularly and intracellularly. This point 

 was confirmed early in the course of the present work, and an attempt was 

 made to determine something of the effect of the pathogen on the individ- 

 ual host cells. Liquid cultures in which the fungus had grown, extracts 

 from mycelium, and alcohoHc precipitates from both of these types of sub- 

 stances have produced no perceptible effect on raw sterile celery when pieces 

 were immersed in such solutions. It was found that enzymes which will 

 dissolve cellulose or pectin and allow the fungus to make progress between 



