DISEASES. 163 



true seeds as worthless when compared to their juicy 

 fleshy envelopes that constitute his favorite fruits, or thu 

 enlarged and succulent roots, tubers, stalks, and leaves, 

 that characterize his garden vegetables and field crops ; 

 while in the grains proper he seeks sustenance in the true 

 seeds, which become the object of his greatest care and 

 ingenuity to enlarge, to increase, and to develope, parti- 

 cularly in regard to their nutritive qualities. 



Most writers upon the diseases of plants have given us 

 very indistinct notions upon the subject, and have done 

 very little to enlighten their readers; while they have 

 written voluminously upon the unhealthy and unsatisfac- 

 tory condition of certain vegetables, and have given us 

 most extensive accounts of the treatment by which they 

 propose to remedy the evils complained of, we gather lit- 

 tle of the information needed to enable us to understand 

 the true state of the case, or of the causes of the disease, 

 if it is to be considered such. The reader need not expect 

 that he will be more enlightened by this chapter than he 

 has been by the essays to which reference is here made, 

 but he will be led to a consideration of some of the causes 

 of those departures from health and vigor which are con- 

 sidered diseased action, and in this way he may possibly 

 be put upon the track which will lead him to the avoid- 

 ance of disastrous results. More than this 'will not be at- 

 tempted. 



Perhaps the most satisfactory account of diseases of 

 plants is that given by Lankester, in which he divides 

 them according to their causes, as follows : 



1st Those produced by changes in the external condi- 

 tions of life, such as redundancy or deficiency of the in- 



