Fabricius • Attempt at a Dissertation on the Diseases of Plants 



123 



complete, but I will be glad indeed, if 

 I can encourage others to make closer 

 observations on this so important part 

 of agriculture. 



The classification of these various 

 diseases is arbitrary; several could be 

 made and for each could be found argu- 

 ments for and against. Hitherto atten- 

 tion has been directed only to that part 

 of the plant on which the disease is 

 observed, yet the same disease can at- 

 tack various parts of the plant; other 

 diseases appear sometimes on one part 

 sometimes on another, while the injury 

 or cause of the disease lies hidden in 

 quite other parts. I will therefore at- 

 tempt a new method and deduce the 

 classes and genera according to the ap- 

 parent cases, but the species according 

 to the causes of the disease. 



Class 1. Rendering unproductive 

 are those cases in which 

 the plants are prevented 

 from setting fruit or are 

 rendered distinctly less 

 fruitful. This is frequently 

 not observed until after 

 blossoming. 

 Class 2. Wasting are those dis- 

 eases in which the plants 

 are slowly killed, their 

 growth and strength grad- 

 ually decreasing. 

 Class 3. Decaying are those cases 

 in which the main parts of 

 the plants are decomposed 

 and become a rotting 

 mass, which by degrees is 

 transformed to mouldy 

 soil. 

 Class 4. Discharging are those 

 cases showing an abnor- 

 mal flow. 

 Class 5. Rendering misshapen, rec- 

 ognized by the abnormal 

 development of the exter- 

 nal parts. 

 Class 6. Extraneous are those cases 

 due to the apparent injury 

 to the parts. 



(Examples From Some of the Classes) 



Class 1- 



-Smut. Ustilago 



Smut on cereals is one of the most 

 common and best known diseases; it 

 often nullifies all hope of a good har- 

 vest. It attacks by preference wheat, 

 barley and oats, while r}'e and millet 

 seldom or never suffer. Eradicating this 

 disease has become the more difficult 

 after recent careful investigations have 

 proved it contagious. When it has once 

 gained the upper hand in a field, it in- 

 creases in strength year by year. Smut 

 only attacks the floral structures which 

 it gradually transforms to a loose black 

 powder easily blown about by the wind. 

 Tillet claims that smut is spread by 

 contagion alone. In this he only up- 

 holds our own opinions in regard to its 

 contagious qualities without showing 

 the real causes. 



Professor Gleditsch, on the other 

 hand, attempts to prove that those ker- 

 nels which have not attained full ma- 

 turity at harvest time, undergo, in their 

 place of storage, a kind of fermentation, 

 from which later, when the seed is 

 sown, smut is derived. How can it be 

 that only a few species of plants are 

 attacked by smut even though unde- 

 veloped seed are to be found in all. 



Two remedies are used to prevent 

 smut on our fields: sowing pure seed, 

 and soaking the seed in a solution of 

 salt or lime. Both remedies are highly 

 praised and indicate, moreover, that 

 the cause of smut is not to be sought in 

 the soil but in the seed. . . . 



Class 4— Rust 



Rust appears both on the stem and 

 on the leaves of plants; it rends the 

 tender covering and hides the surface 

 under a brownish and light powder. 

 Often it only occasions small spots on 

 the leaves and affects the development 

 of the plant but slightly. However, 

 when it gains the upper hand and at- 



