322 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



useless, but successive crops of the same potato on the same land 

 are certain to be attacked, and it is impossible to grow varieties of 

 potato which are liable to this disease for several years without the 

 certainty of their being attacked. Fortunately, however, there are 

 several varieties of potato which are absolutely immune to the Wart 

 Disease, and these are the only sorts which the Board of Agriculture 

 allow to be planted on land which has once been affected by the 

 Wart Disease. 



Nothing perhaps is more interesting or remarkable in the experience 

 of potato-growers than the striking immunity of such sorts as ' Lang- 

 worthy,' ' Sutton's Supreme,' ' Conquest,' ' Abundance,' ' What's 

 Wanted,' ' White City,' and ' Great Scot ' to the attacks of Synchytrium 



cndobioticum. 



Mr. G. Massee pointed out that the effect of different minerals 

 or fertilizing substances as affecting the relative susceptibility of 

 plants to injury by fungi was not a new idea. As a boy on his father's 

 farm he learned from others that the use of nitrate of soda favoured 

 the development of rust on cereals, more especially barley. 



He drew attention to the following points in relation to diseases 

 of plants caused by fungi : — 



Fungi in general are to-day credited with doing much more 

 harm to plants than they do in reality. Apart from the rusts, smuts 

 and mildews, it is an open question as to how many fungi are the 

 primary cause of disease, but given a chance due to some previous 

 weakness on the part of the host-plant, such fungi can gain a foot- 

 hold and work havoc, and as such havoc is obvious the fungus is too 

 frequently considered as the primary and sole cause of injury, whereas 

 but for some previous weakness the said fungus could not have attacked 

 the plant. In such cases fighting the fungus does not strike at the 

 root of the matter, and good results cannot be attained, as everyday 

 experience abundantly proves. 



The favourite occupation of working out the so-called life history 

 or cytology of a fungus, although valuable in proportion to its accuracy, 

 does not indicate the primary cause of disease, which in the majority 

 of cases — except in the rusts, smuts, and mildews — is a physiological 

 problem, a problem invariably shirked, probably on account of the 

 difficulties it embodies. There must be a definite reason why certain 

 plants remain immune when every chance of infection is present. 

 To select and breed from such immune specimens is a rule-of-thumb 

 method. The "why" is the question to be settled once for all, so 

 as to give the clue. A better knowledge of plant physiology appears 

 to be the only hope for elucidating the matter, and should be for- 

 warded at all costs. Plant pathology, so far as fungi are concerned, 

 can only state, with more or less accuracy, the fungus present, and 

 suggest means for preventing its spread. 



He had no doubt that immune plants can be produced in any 

 given place if sufficient attention is given to the subject, but common 

 experience has proved that such plants, when cultivated at a distance 



