27 



CROWN GALL. 



(Bacterium tuinefaciens.) 



The swellings or galls termed Crown Gall occur on a great, 

 variety of herbaceous and woody plants. They are abundant, 

 on various kinds of nursery stocks, particularly apple stocks, 

 but, amongst fruit, pear, quince, plum, cherry, apricot, peach, 

 raspberry, loganberry and blackberry also suffer, and in 

 America bad cases have been noted on gooseberries. Plants, 

 of many other kinds are attacked, chrysanthemum, hollyhock, 

 beet, mangel, and amongst stocks other than fruit trees, 

 Itanetti roses axe particularly susceptible. The disease 

 is now found in most parts of the British Isles, nurseries 

 having" distributed affected stocks not only all over England, 

 but to many other parts of the world. Although not so serious- 

 in its effects as are most diseases the health of plants attacked 

 by Crown Gall usually suffers sooner or later, the effects 

 being seen in dwarfing of growth or direct injury to roots 

 or branches, some plants being more seriously affected in this 

 way than others. Apart from actual injury, the disease 

 causes the, plants to appear unsightly and renders the stock 

 unsaleable. For this reason it is important to take what steps 

 are possible to control the disease. 



It should be noted that galled plants will not be certified 

 for ej-pott, hence special attention to preventing attacks 

 should be given by all growers of fruit trees, roses and other 

 plants for export to America or other countries. 



Cause of the Disease. Crown Gall has been known for 



very many years and has been the subject of much speculation 

 and investigation, but only comparatively lately has its true 

 nature been discovered. The disease in all its forms and on 

 a large number of plants has been the subject of the most 

 intensive study for over fifteen years by Dr. Erwin F. Smith 

 and his colleagues in the Department of Agriculture at 

 Washington. They have proved beyond question that the 

 disease is infectious and is caused by a bacterium which they 

 have named Bacterium tumefaciens. The galls can be produced 

 at will by inoculating appropriate tissues of healthy plants 

 with cultures of the bacterium. The bacteria are excessively 

 difficult to see in the tissues of the galls and, hence, for long- 

 escaped recognition. The American work has, however, quite 

 recently been confirmed in England in the case of the Paris 

 Daisy (Chrysanthemum frutescens); the same bacterium has 

 been isolated and inoculations with the organism have produced 

 new Crown Galls. * Further work on the Crown Gall is being 

 pursued in this country at more than one research institute. 

 On the practical side the disease is being investigated at the 



* Ann. BoL, Vol. XXXV. pr. 137-8. 



