2o6 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



of an old forest, on the 26th February 1900, and again in the 

 middle of March 1900 in the leaves of a thicket, both closed 

 and open apothecia, whereas those observed in young cultures 

 were almost all still closed and remained so till April. 



Von Tubeuf 's obervations are valuable, but the conclusion he 

 draws that the apothecia found open in April can expel germs 

 after every rain throughout the summer requires modification. 



The expelling of germs is not dependent on rain. The 

 apothecia empty themselves of all germs in a short time, under 

 the influence of sufficient moisture, and cannot go on all summer 

 with the process of fructification. That by careful searching 

 open apothecia containing fertile germs can be found here 

 and there in every month of the year must be admitted, but 

 it is contrary to the facts of the case to say that they are as 

 a rule fully developed as early as April. Such cases are 

 exceptions. This can be fully ascertained by careful prolonged 

 study of the disease on selected areas during all periods of the 

 year, especially in young cultures. The leaves infected during 

 the summer begin to redden about the end of September. 

 During the winter months the progress of the disease is slow, 

 but in spring it advances rapidly and soon causes shedding of 

 the leaves (hence the German name Schiielte.) 



It is these leaves shed in spring which cause the spread of 

 the infection in the summer. When they fall in April and May, 

 no apothecia (with rare exceptions) can be observed. The latter 

 form only in June and July, ripening from about the 15th of July 

 onward. By the beginning of October they have exhausted 

 their supply of germs, which they expel very rapidly under 

 suitable conditions. 



When the conditions are adverse the ri[)ening may be 

 delayed in some instances, but these late coiners are of no 

 practical importance. It happens even more rarely that special 

 conditions cause a premature ripening of apothecia, causing 

 them to open in winter and early spring. It was these that 

 von Tubeuf found in April on newly cultivated areas. They 

 are of no practical importance, for the ripe apothecia must 

 open as soon as there is sufficient moisture, and the germs, 

 once expelled, have a short life. They either grow at once or 

 not at all. 



The formation and ripening of apothecia on the leaves of 

 older trees is more complicated than on the young growth. 



