29 



Once inside the tissues the bacteria multiply, but instead 

 of destroying the cells they stimulate them to divide and en- 

 large, much in the same way as the Wart Disease fungus does 

 in the case of the potato tuber, and a gall or tumour is 

 produced. Crown Gall is, however, peculiar amongst plant 

 parasites, in that, in certain plants at any rate, the affected 

 areas form strands (termed tumour-strands) in the healthy 

 tissue along which the bacteria travel, and from which other 

 galls arise, sometimes at a considerable distance from the 

 original gall. This fact explains why it is that new galls arise 

 in other spots if the primary gall is removed. 



Extent of Injury. The amount of damage caused by 

 Crown Gall varies greatly in different crops. In some cases 

 it is almost negligible. Stone-fruits suffer more than apples or 

 pears. Soft fruits such as raspberries have been so injured in 

 Sweden a to bear practically no crop and similar cases have 

 been recorded in England. On the vine Crown Gall 

 is regarded as a serious disease in France and Italy. Manetti 

 roses, which are singularly subject to attack (see Fig 2), are 

 said to be much impaired for the uses for which they are 

 .required in America. 



Few precise data have yet been collected in this country on 

 the nature and extent of the injury which is caused. In apples, 

 recent work tends to show that its effects are comparatively 

 slight and not so serious as was at one time thought. The 

 amount of injury varies in different varieties, not only as 

 regards the stock, but with the variety of apple grafted on it. In 

 America affected trees are liable to be retarded in development 

 and dwarfed in growth. Early death sometimes takes place. 

 The root system is often interfered with, as a result of which 

 the trees suffer. On the other hand, in some cases the stocks 

 appear to be able to throw off the disease entirely. In England 

 it has been observed that during tEe first few years after plant- 

 ing galled trees often grow almost, if not quite, as well as 

 trees free from galls. The amount of injury which takes place 

 depends largely on the position of the gall on the tree, galls 

 at the crown, for instance, being more serious than those on 

 lateral roots. Those galls, moreover, which have a narrow 

 neck are less harmful than those which are attached by a 

 broad base. 



In addition to direct damage Crown Gall may be dangerous 

 in that it affords a means of entry for various 'parasitic fungi. 

 Further, the distribution of diseased stock among new and 

 clean orchards may lead to serious injury to other plants such 

 as raspberries and loganberries, which may subsequently be 

 planted. It is quite plain, therefore, that the disease cannot 

 be disregarded. Galled plants cannot be exported and will 

 not be accepted readily by buyers at home. 



