INJURIES INDUCED BY PLANTS 143 



In the great majority of cases the gonidia appear to be doubly 

 septate, although occasionally one meets with singly septate 

 examples, and even unicellular gonidia are not unknown. They 

 are of a pale brown colour, and germinate in a few hours, 

 pushing out a thick germ-tube from both ends (Fig. 80, 6). 



The parasite is distributed in May and the beginning of June 

 by means of the gonidia, which are washed by the rain from 

 the higher diseased shoots on to the young shoots of the lower 

 part of the crown. In other cases the wind may carry them on 

 to distant maples. 



This destructive parasite of our gardens and parks can only 

 be combated by removing the diseased shoots from the crown in 

 the beginning of May. 



SEPTORIA PARASITICA, THE SPRUCE-SHOOT DISEASE 1 



Both in young spruce woods and in the seed- and plant-beds 

 of the nursery a disease, which on a cursory examination may 

 easily be mistaken for damage by frost, very frequently attacks 

 the young shoots. 



In the month of May, when the young shoots are still succu- 

 lent and delicate, the disease generally manifests itself (see 

 Fig. Sly a) by the leaves at the base, or it may be the middle, of 

 the shoot becoming brown and soon dropping off. At first the 

 apex of the shoot remains quite green, but on lateral branches 

 it droops downwards. The disease advances rapidly towards 

 the apex of the shoot, and the base of the young leaves appears 

 dark green (Fig. 81, b). When held up to the light, it will be seen 

 that the internal tissues of the leaf are dead and shrivelled, and 

 possess a reticulated appearance. Finally the leaves all drop 

 off, or a few dead ones may adhere to the apex of the shoot, as 

 indicated in Fig. 82, a. The axis of the shoot shrinks more or 

 less according as death had overtaken it in an early or late stage 

 of development. Very frequently the shoot becomes diseased 

 and begins to shrink at the point where its base is enveloped by 

 the scales of the previous year's terminal bud, and this often 

 occurs in the case of shoots that are tolerably well developed. 

 The base of the shoot shrinks, and its internal tissues are so dis- 



1 R. Hartig, Zeitschrift filr Forst- und Jagd-wesen, November 1890, p. 668. 



