112 Butler-—A Study on Gummosis of Prunus and Citrus, with 
and almond were very sensitive to wound stimuli, but the cherry, plum, and 
apricot were less responsive and gummed less readily. When, at the height 
of the growing season, shoots of peach and almond were wounded into the 
cambium and secondaty wood, at intervals, beginning from the apex, drop- 
lets of gum were observed pearling at some of the wounds in less than 
a week, sometimes even in four days. Dividing the affected shoots into 
zones they found that gum production was closely related to the position 
occupied by the wounds on the shoots. At the apices gummosis was 
slight, then rapidly reached a maximum, decreased again, and finally ceased. 
The zone of maximum gum formation occurred just beneath the region 
of maximum growth in length, and was probably correlated, Beijerinck and 
Rant believed, with the growth in thickness of the cambium, and also 
of the procambium. 
When shoots were wounded during the course of the summer, but after 
suberization had taken place, they generally failed to produce gum. In this 
case the production or non-production of gum appeared to be correlated 
with seasonal peculiarities. 
The gum was formed in the young wood in formation and the diseased 
tissues, while young, always abutted directly on the cambium. The length 
and importance of the gum pockets depended largely upon the size and 
position of the wound upon the shoot ; their distal ends were always further 
removed from the centre of propagation than their basal ends. Wood 
normally formed never produced gum. The gum pockets buried in the 
wood were formed by cambial activity at some previous time, and a series 
of gum pockets in a single season’s growth were due to conditions being 
such that the cambium laid down normal and abnormal embryonic xylem 
alternately. 
Beijerinck and Rant obtained some interesting results with corrosive 
sublimate and burning as the stimuli of gum formation. When mercuric 
chloride was introduced into wounds made on young growing shoots of peach, 
abundant gummosis occurred after the lapse of four to sevendays. Burning 
was also effective, but not as much so as corrosive sublimate, probably 
owing to the fact that the area of tissue stimulated was less extensive than 
in the case of the latter, the burns being produced by focusing the sun’s 
rays upon the shoots. 
Gummous degeneration of the tissues Beijerinck and Rant believed to 
be due to a cytolytic enzyme becoming active the moment necrobiosis set 
in. In necrobiotic cells the protoplasm was killed, but the enzyme remained 
alive and active, and was able to diffuse out into the surrounding tissues, 
which it transformed into gum. The greater gum flow when mercuric 
chloride was used than when the tissues were simply burned or only 
wounded lent support, they believed, to this view. The gumming of tissue 
infected by Coryneum Beyerinckii, the hyphae of this parasite only showing 
