PUCCINIA GRAMINIS 43 



by its uredospores, (2) by a perennial mycelium, (3) by Eriks- 

 son's mycoplasm. 



The first possibility is entirely a matter of climate : it may 

 take place in one country and not in another, or in the same 

 country it may take place in one season and not in others. 

 McAlpine and Cobb find viable uredospores all the year round 

 in Australia, and Lagerheim says the same for Ecuador. But 

 in northern climates it has been shown that the uredospores of 

 P. graminis frequently lose all capacity for germination during 

 the winter ; this is proved true of Sweden, North Germany, 

 North Dakota, etc., but in the United States, south of Ohio, 

 Bolley found germinable uredospores all through the year. 

 Similarly in Bohemia, uredospores of P. dispersa, P. glumarum 

 and P. Lolii can survive mild winters or in sheltered places 

 (Baudys). Even though uredospores capable of germination 

 may sometimes be found on wild grasses during the winter, it 

 does not follow that those could start an epidemic next spring, 

 owing to the specialisation which has been proved to exist, by 

 which a form of P. graminis on one host is often incapable of 

 infecting another host. 



In regard to the second possibility, we find again two 

 opposing views. De Bary and others have searched in vain for 

 mycelium in the growing wheat plants, before infection becomes 

 visible, but Pritchard (1911) found mycelium resembling that 

 of P. graminis both in the pericarp of w T heat grains and in 

 various parts of wheat seedlings. He showed that large num- 

 bers of wheat grains contained pustules of teleutospores, even 

 visible in the neighbourhood of the hilum, but also hidden 

 within the pericarp. He proved that the mycelium from the 

 pericarp penetrates through the intercellular spaces, as well as 

 through the cells, and " soon passes into the spaces between 

 the leaf-sheaths where it grows rapidly and attacks the tissues 

 at various points." W. G. Smith figures teleutospores within 

 the seed of Oat (Gard. Chron. 1885, xxiv, 245, f. 53) and recidia 

 in the pericarp and seed of Barberry (ibid. 1886, xxv, 309, 

 f. 58). 



It is evident that, if this state of things prevailed on a 

 large scale, nothing more would be required to explain the 



