39 



RUST RESISTANT VARIETIES. 



Jethro Tull* remarks that " the white cone wheat, which hath 

 its straw like a rush full of pith, is less subject to blight than 

 Lammas wheat, which ripens a week later." There does not 

 appear to be any special allusion to the rust-resisting powers of 

 varieties of wheat in the replies to the inquiry instituted by the 

 Board of Agriculture in 1804. Neither is there much informa- 

 tion afforded in the answers to the questions sent by the Royal 

 Agricultural Society in 1883, except that Rivett, Lenny's White, 

 Browick Stand-up, and Red Chaff White, were less affected 

 than other varieties, such as Scholey's Square Head, Golden 

 Drop, Nursery, etc.j 



It is somewhat remarkable that though Scholey's Square-head 

 is shown to be liable to mildew by the Royal Agricultural Society's 

 Report, it was found to resist it better than any other variety in 

 1891, in Germany, where it is largely cultivated, having super- 

 seded all German varieties. M. Georges Ville says of the 

 Square-head variety, " Two circumstances explain the favour 

 without parallel, I believe, in the history of wheat which 

 attaches to the Square-head. In the first place the resistance of 

 the straw to laying, and to the action of parasitic fungi, espe- 

 cially rust ; these qualities are inseparable. Everyone knows 

 the close relation which exists between the appearance of a 

 parasite and the texture of its host. The straw, which is bent 

 under the weight of the ear, is formed of a yielding succulent 

 tissue, which opposes but a slight obstacle to the penetration of 

 the mycelium of the parasite. The Square-head, bora under the 

 humid sky of Britain, possesses in the utmost degree the faculty 

 of consolidating its mechanical system under the influence of 

 the more variable climate of the Continent."^ 



Most valuable researches have been made in Australia by Dr. 

 Cobb as to the causes of certain varieties of wheat being less 

 liable to rust than others. Dr. Cobb made a series of observa- 

 tions on the number and size of the stomata, or breathing pores, 

 because it was imagined that the structure of the stomata must 

 have an important bearing on the entrance of the promycelium 

 of rust. He found that the number of the stomata upon the 

 leaves of wheat varied from thirty-eight to seventy-five per 

 square millimetre. In general the stomata w r ere smaller and 

 more numerous, while on nearly all leaves the number of 

 stomata was fewer by abour 10 per cent, on the ; 'lower surlace 

 than the upper. Nevertheless the smallest stomata were 

 observed to be large enough to admit the entrance of the 

 promycelial thread of rust. Dr. Cobb saw enough to convince 

 him that rust had entered freely through the smallest stomata 

 observed. As many as fifty spores per square millimetre were 

 noticed on the upper surface of the leaves, and about twenty- 

 five per square millimetre on the lower surface. 



c Horse-Hoeing Husbandry, by Jethro Tull, 17. 



f Report on Wfieat Mildew, by W. C. Little, R. A.S.E. Journal,vol. xix., sec. ser. 



j The Perplexed Farmer, by Georges Ville. 



