76 REPOET OF THE COMMISSIONER OF AGRICULTUEI' . 



FUNGOUS DISEASES OF PLANTS. 



[This chapter, giving outliiK s of certain fungous diseases of plants, with remarks 

 i;;iOu the ai)plicatiou of remedi e, w .s prepared by the Aosistant Botanist, F. Lainsun 

 S.--ibnrr.] 



It- is tlic puq>ose of this chapter to present in genornl terms tbe ieaci- 

 ins characters of some of the chief groups or more destructive species 

 of fungi,* a knowledge of which is of the first importance in seeking 

 means for their destruction. It will be understood, of course, that there 

 are many x)lant diseases which must receive special investigations, both 

 in the field and in the laboratory, before any definite conclusions can be 

 reached respecting their nature or the remedies that should be employed 

 against them. 



In spite of the fact that our cereal and other crops of the farm and 

 orchard are damaged to the extent of many millions of dollars annu- 

 ally by the attacks of fungi, there has been very little done towards in- 

 stituting experiments to find means to guard against them. They are 

 scarcely less destructive than are our inject foes, for there is hardly a 

 plant that does not support at least one of these minute parasites, while 

 the greater number are obliged to nourish a score or more. 



The injury they occasion has generally been accepted as inevita- 

 ble. People have seen their crops destroyed by the several blights, 

 the various mildews, the numerous rusts, smuts, and early rots, all 

 diseases caused by fungi, and have stood by inactive, deeming them- 

 selves powerless to prevent these things. This feeling has been fos- 

 tered by the assertion that these diseases were wholly due to atmos- 

 pheric causes — an expression so frequently made and insisted upon that 

 it has become the settled belief of many. Ivecent progress in botanical 

 science, however, has demonstrated the fallacy of this view by discov- 

 ering the real sources of the evil, and what was formerly involved in 

 mystery is now known to be due to a class of objects which, in their 

 growth and development, are amenable to the same laws that govern 

 all organic bodies. These objects may be compared to weeds, which 

 instead of robbing useful plants of their food supply in the soil, take 

 directly from the plants themselves the food they have prepared for 

 their own nourishment. 



We must not commit the error of assuming all plant maladies to be 

 due to fungi. Other causes may produce disease, and the question of 

 determining this cause is by no means so easy as some suppose ; in gen- 

 eral terms, however, plant diseases may be classed as, 1st, those arising 

 from physical or chemical causes ; 2d, those due to the attacks of iu- 

 se(;ts ; and 3d, those occasioned by fungous parasites. These several 

 causes may unite in bringing about a diseased condition of a plant so 

 that it becomes impossible to assign the origin of the trouble to either 



* A fungns (plural fungi) is a plant of low organization, having a vegetative and 

 rci)roduciive system, but wholly destitute of green coloring matter (chiorophylle). 

 Tbo species are either parasitic, feeding on living plants or animals, or sapropnytic, 

 deriviug their nourishment from dead or decaying substances. 



The vegetative system generally consists of elongated, slender, thread-like cells, 

 or hyphaj, collectively termed mycelium. The mycelium of the parasitic species 

 grows either upon or within the tissues of the plant— called the host plant — support- 

 ing it. There is much similarity in the mycelium of the different fungi, but in the 

 reproductive system there is great diversity, and the peculiarities of structure and 

 development in the fruit afford the essential characters of classiflcation. Whatever 

 the diversity may be, however, in the reproductive system, the universal object is the 

 formation of the sporo, an organ analogoos to the seed of higher plants. 



