440 



BOTANY OF THE LIVING PLANT 



uncertain. It is significant that Wheat-Rusts abound in South 

 Africa, Australia, and parts of India, where no species of Berberis 

 are indigenous. The most effective remedy is to plant only the seeds 

 of varieties of wheat that are known to be immune to the disease, 

 by resisting the infection. Progress has already been made in the 

 production and circulation of such immune varieties. But owing 

 to the minute specialisation characteristic of many Rusts a variety 

 may be immune in one country and susceptible to the same Rust 

 in a different climate : so delicate is the balance which exists between 

 the attacking and resistant powers of two organisms. (Compare 

 Chapter XII., on Irregular Nutrition.) 



USTILAGINALES (SMUTS). 



The Smut-Fungi (Ustilaginales) are also parasites on Grasses, 

 certain of them causing diseases on Oats, Barley, Wheat, and Maize, 

 which culminate in the fruiting Ear. The diseased grain is replaced 

 by a mass of dusky spores, corresponding in their behaviour to the 

 teleutospores of the Uredinales (Fig. 339). For like them they ger- 



Fig. 339. 



Teleutospores or brand spores of Ustilago germinating, and giving off basidiospores 

 or sporidia. (a) germinated in water only, b, c, d, e in nutritive solutions, where they 

 continue to sprout. Very highly magnified. (After Brefeld, from Marshall Ward.) 



minate after the winter's rest, forming a basidium (promycelium) with 

 effective basidiospores (sporidia). The germs may have remained 

 in the soil of the field from the previous season ; or the crop may 

 have been harvested and the straw used for bedding, passed to 

 the manure-heap, and then carted out on to the land again. Either 

 way the soil in which the grain germinates will have been infected. 



