586 Brooks .— The Development of 
time when the new foliage was appearing, cherry-leaves containing the ripe 
perithecia of the fungus—likewise obtained from Kent—were damped and 
hung on the trees. Frank has shown that the perithecia when alternately 
damped and dried liberate their spores by successive ejaculations. I con¬ 
firmed this by placing damp leaves bearing perithecia in Petri dishes ; when 
the leaves had become dry it was found that the ascospores had collected in 
groups of eight on the lid of the dish. Thus when leaves bearing mature 
perithecia were damped and hung on the trees it was considered that the 
conditions approximated to those under which infection ordinarily occurred 
in nature. Later on in the summer it was found that a few leaves had 
become infected. The number of infected leaves, however, was insufficient 
to provide material in different stages, so several journeys were made to 
Kent for the purpose of obtaining further supplies. During these visits 
some observations were made on the relative susceptibility and immunity 
of different cultivated varieties of Cherry trees. It was found that the 
following kinds of sweet cherries are attacked by the disease to the greatest 
extent:—Florence, Waterloo, and Frogmore, while Elton Heart and Black 
Heart are only slightly attacked, and Amber, Turk, and Crown varieties are 
apparently immune from the disease. 1 These observations are in agreement 
with those of Salmon (27). 
Thus the ‘ Cherry Leaf Scorch ’ is another of those diseases which affect 
different cultivated varieties of the host species to very different degrees. 
As yet, practically nothing is known as to the factors which confer immunity 
upon some varieties. 
Upon making inquiries I found that the c Scorch ’ disease is now much 
less prevalent in Kent than formerly. This is due to the commendable 
practice in many orchards of destroying from year to year the leaves found 
hanging on the trees in winter. It has been well known since Franks first 
account of the disease, that the leaves which hang on the trees in winter are 
the only means by which a new infection can take place. 
In one or two plantations visited, these measures had not been taken for 
the destruction of the disease. It was here noticeable that the trees 
susceptible to the disease produced only a very meagre quantity of fruit—• 
the natural consequence of the weakening of the trees by the presence of the 
fungus for several years—and the cherries that were formed became hard, 
distorted, and spotted. Such cherries never became properly ripe. 
External Appearance of Leaves affected by the Parasite 
in its Early Stages of Development. 
Great difficulty was experienced at first in finding leaves in the early 
stages of attack. Little help was obtainable from Frank’s account as 
1 Acid cherries also remain free from attack. 
