DISEASES OF CROPS. 



pests! Happily our English farm crops Lave not such 

 an array of deadly foes as the vine. The wheat has its 

 " mildew," its " smut,'' its " canker," besides such animal 

 foes as the corn-weevil, the corn fly, the wire-worm, and 

 the Hessian fly. The potato has its Peronospora, its 

 Colorado beetle, etc. 



The mildews and other fungi which infest farm crops 

 are all " built " more or less upon the same structural plan. 

 They take their origin in spores which are found in the 

 atmosphere, soils or water. The spores give rise to 

 hyphce (filaments), which live principally upon the albu- 

 minous substances found within the living cells of various 

 farm crops. Each hypha (in the majority of cases) is 

 composed of a variable number of microscopic cells placed 

 end to end, and each cell is composed of an external wall 

 or covering of a peculiar kind of cellulose, and contains 

 a living granular substance called protoplasm (" the basis 

 of life "). The cellulose of parasitic and saprophytic fungi 

 is of a different nature to that found in the higher plants. 



The hyphsB (produced fi-om spores) branch and become 

 closely interwoven and twisted in all directions. This 

 '' mat-like " mass of hyphse is called a mycelium,^ and 

 gives rise to elongated cells springing vertically in the 

 air, bearing, at their free ends, spores. 



As fungi, unlike the higher plants, contain no chloro- 

 pliyll (green matter), they are incapable of living upon such 

 inorganic or mineral substances, as atmospheric carbonic 

 acid gas, water, ammonia and various soluble salts. Be- 

 cause they are incapable of "manufacturing" albumin. 



• There is no connection between cells, which are in apposition in 

 two separate hyphse. This is one of the distinctions between fungoid 

 " tissues " and those of higher plants. 



