WHEAT. 95 



scopical observation shows the fungus to be totally 

 different in its form and growth from the grain fun- 

 gus, and, therefore, that the one species cannot pro- 

 ceed from the other. Some have supposed that, in- 

 stead of being a fungus, the rust of wheat is merely 

 an exudation of its juices through the ruptured ves- 

 sels of the plant, and that this loss of sap occasions 

 the shrinking of the grain. 



Considerable observation of the state of grain 

 previously to, and during the appearance of blight, 

 and the microscopical growth and spread of the rust 

 or fungus, have induced us to suppose that in most 

 cases the operation of both these causes, viz., the 

 bursting of the vessels and the spread of the fungus, 

 are present in blight. The rust usually appears first 

 in patches on the leaves ; and it spreads to the stalks 

 of the wheat only when the state of the weather 

 and of the plants is such as to justify the supposi- 

 tion of the exudation of sap. If the stem is partially 

 dried or ripened, the sporules or seed of the fungus 

 seem spread over its surface in the exuded but dried 

 sap, like a reddish or yellow varnish. If the stem 

 is green (as in the case of late-grown or winter-killed 

 grain) at the time of attack, the flow of sap con- 

 tinues through the ruptured vessels, and the spo- 

 rules, finding in this moisture a convenient nidus or 

 place of growth, penetrate the openings with their 

 roots, and assume the linear appearance so charac- 

 teristic of this disease. The rapid propagation of 

 this fungus will not be matter of wonder when it is 

 remembered that it passes through its stage of 

 growth and ripening its seeds in little more than 

 twenty-four hours ; and that, according to Ehren- 

 burg, some species of fungi contain 250,000,000 of 

 seeds. The minute particles that make the smoke 

 of the common pufif-ball are the ripened seeds of that 

 fungus ; and those of the Uredo are so small as to 

 be undistinguishable, except in masses, without the 

 aid of the microscope. If the rupture of the vessels 



