PLANT DISEASES. 



725 



farmer has to deal that the signijficant shake of the head, implying 

 incredulity, on the part of anyone told for, the first time that a fungus 

 may occur under forms as different in appearance from each other as an 

 Oak-tree, a Poppy, and a Water-Lily respectively, during different periods 

 of its complete life-cycle, or that it spends part of its life as a parasite 

 on one particular kind of plant, and then moves to another plant, not in 

 any way related to the one it previously lived upon, to complete its career, 

 is, to say the least, quite pardonable, and furthermore displays the right 

 spirit in not accepting such a strange doctrine without some more 

 convincing proof of its verity than the mere statement, granting that 

 prejudice does not harden the heart and close the mind againat accepting 

 absolute proof when tendered. 



The above illustrations, along with many other facts equally strange- 

 sounding when heard for the first time, add considerably to the ordinary 

 difficulties experienced in grasping the broad principles of a subject 

 entirely novel ; and I hope to be pardoned for stating my experience that 

 the majority of practical men have reached such a high pitch of per- 

 fection, in successfully carrying out those branches of their profession 

 which they have thoroughly grasped, that there is more than an indi- 

 cation of the feeling that what they do not already know is not worth 

 consideration. 



This feeling is at the present day fast disappearing, however, and 

 there is a manifest desire on the part of most of the rising generation to 

 accept the inevitable, and gain more than a simple rule-of-thumb 

 knowledge respecting the diseases to which plants are subject. 



There is a deep-rooted opinion that cultivated plants are more 

 susceptible to disease than wild plants are, and certain appearances seem 

 at first sight to support this view. There is, however, no scientific 

 support for this idea, and most of the apparent evidence may be traced to 

 the fact that many parasitic fungi confine their attacks to one particular 

 kind of plant, or to plants closely allied ; hence, for instance, in the case 

 of a large house crozcded with Tomato plants, if a single plant, to 

 commence with, is attacked by Cladosporium fulvum, the disease will 

 gradually spread from this one plant until every plant in the house is 

 diseased, unless prompt measures are taken to prevent the spread of the 

 fungus. Now in this instance, if the plants are well gro^vn, there is no 

 special predisposition to disease proved by the fact that all the plants are 

 attacked ; it simply means that the fungus found a lot of plants of the 

 particular kind it could feed upon, huddled together so that it became an 

 easy matter to pass from one to another. Epidemics or wholesale 

 destruction caused by fungi never occur in houses or elsewhere where the 

 plants are of many different kinds. 



It may be argued, and with reason, that crops, or assemblages of one 

 particular kind of plant, must of necessity be grown over more or less 

 extensive areas ; nevertheless, the fact remains that this massing together 

 of numbers of the same kind of plant is responsible for practically all 

 fungous diseases that occur on a large scale. 



Admitting the fact that plants of the same kind must be grown 

 together in large numbers, what the gardener can do is to use proper 

 precautions to prevent the spread of a given disease the moment it 



