Nov. is, 1920 Vascular Discoloration of Irish Potato Tubers 285 



Another striking thing brought out in Table II is the frequency with 

 which Alternaria was recovered from the vascular tissue. Almost 20 

 per cent of the discolored tubers carried this genus, in most instances 

 unmixed with other fungi. This proportion is so high as to suggest that 

 it may possess some significance hitherto unsuspected or at least undis- 

 covered. Similar results have frequently been secured with other 

 material. As high as 50 per cent of some lots of tubers have yielded 

 Alternaria in cultural tests, even from stock presenting an attractive 

 appearance on superficial examination. 



FIELD STUDIES 



The general manner in which the stock was handled in planting has 

 already been indicated (p. 277-278). In taking notes in the field a full 

 description of each plant was recorded at each reading, including such 

 matters as size, habit, character, color, and orientation of stems and 

 foliage, as well as the general appearance as to vigor. At least three 

 sets of notes, and in the case of some lots more, were made on each plant 

 during the season. Successive sets of notes were taken by different 

 members of the staff, and no reference to the previous notes was made 

 while preparing the new set. In the preparation of the present article 

 the writer has endeavored to translate these descriptions into the ex- 

 pressions "diseased" and "healthy." Every plant has been placed in 

 one group or the other, even though in some cases the assignment had 

 to be more or less arbitrary. Consistency has been maintained, however, 

 and the writer has been able to bring to his aid thorough familiarity 

 with the appearance of the material throughout the season. One of 

 the three principal sets of notes is his own. 



Plants whose description at any given note taking indicates probable 

 suspicion in the mind of the observer of the presence of disease have been 

 recorded as diseased, even though at previous or subsequent note takings 

 they may be recorded as healthy. It is certain that many cases of 

 recorded disease at the first note taking represent only delayed germi- 

 nation, but as this may be correlated with reduced vitality or fungous 

 attack on the sprout or tuber, it seems important to record it. Records 

 of recovery as well as of disease have been made and will be considered 

 later, but it is of interest first to inquire into the general relation of 

 vascular discoloration to fungous invasion and the correlation of these 

 within the tuber with disease in the plants produced. For the purpose 

 of this consideration plants once reported as diseased have been counted 

 as diseased whether later reported as diseased or healthy. 



