16 



and are still augmenting the peculiar ingredients for the 

 formation of the seed. The plant is blooming, or near doing 

 so ; the ears, husk, and skin of the grains are formed, waiting 

 to be fertilised and filled, when the fungus steps in and impedes 

 or intercepts the process. 



Its agents, the mycelium threads, are widely dispersed 

 through the whole plant ; they appropriate from the sap the 

 ingredients suitable for themselves, swell greatly, and with the 

 multitude of sporangia forming, choke the channels of the sap, 

 preventing its ascent to the head, where it is reqviired, and 

 finally bursting the skin, the plant is prematurely killed, while 

 the fungus, shedding myriads of spores, has completed its own 

 cycle. 



Should cold, calm, rainy weather prevail at the time the 

 spores are shed from the intermediate plant (or, on the other 

 hand, those of the first stage on the wheat or other plant), the 

 chances are that the greater number of the spores will be 

 washed down into the soil and perish for want of proper 

 nourishment, few only reaching their destination to do any 

 perceptible harm, although the wheat might be in a fitting 

 condition to receive them. Again, should dry weather prevail, 

 with only sufficient moisture in the ground to keep the wheat 

 in a healthy state, the stalks, &c, would be healthy and able 

 to prevent the entrance of the fungi. Yet, a few always escape 

 destruction, or find a suitable host, and a single spore produces 

 a progeny in one season to infect, under favourable circum- 

 stances, a whole field in the next. 



The reason why barley, oats, and some other grasses are not 

 affected at all, or only to a slight degree as far as their seeding 

 is concerned, is to be sought for in the fact that their grains 

 are nearly perfected before the fungus interferes by choking 

 the sap-canals, the latter thus only appropriating their surplus 

 of sap, while in the case of the wheat the fungus comes first. 

 Another cause may be that neither barley nor oats have been so 

 highly refined through artificial selection as wheat, and thus 

 remain hardier. 



The first time the writer observed Red Rust was in 1851-5, 

 near Lyndoch, extending over irregular patches of ground of 

 considerable extent. Where observed it developed most in 

 soils rich in humus and clay, least on stiff loamy soils ; again 

 more so on land ploughed shallow than on deeply-ploughed 

 ground ; but this, most likely, depends upon the subsoil, which, 

 at the spot referred to, was beyond the reach of the plough, 

 and consisted of stiff yellow clay. Since then it has been 

 noticed nearly every year to a greater or less extent, the 

 writer having lived constantly among farmers and farms. 

 In 1862 rust was observed in the neighbourhood of Mount 



