juneis,i92o Relation of Rust in Seed Wheat to Seedling Infection 263 



EFFECT OF KERNEL INFECTION UPON GERMINATION 



Large numbers of rust-infected wheat kernels were germinated and 

 grown to various stages of development for the purpose of making histo- 

 logical studies. Parallel series of unrusted kernels from the same seed 

 lot were germinated and grown for comparison. In these series it was 

 noted that the rusted and unrusted seed gave practically identical 

 percentages of germination. 



RUST TRANSMISSION WITH SEED GRAIN 

 HISTORICAL DISCUSSION 



From the vast amount of work which has been done upon this problem 

 it is possible to separate three main theories. Briefly stated, these 

 theories are as follows : (i) Mycoplasm theory of Eriksson ; (2) dormant 

 mycelium in the seed carrying infection to the seedling; and (3) seed- 

 borne spores causing infection of the seedling. 



MYCOPLASM THEORY OF ERIKSSON 



Eriksson (9) in 1897 announced his well-known mycoplasm theory. 

 He states that in the summer of 1893, upon microscopical examinations 

 of sections of very young sori of yellow-rust (Pticcinia glumarum) upon 

 wheat leaves, he found adjacent to these sori, besides the usual cell 

 elements, peculiar, elongated, mostly faintly curved, plasmatic corpuscles. 

 He concluded {p. jqj, translation) that — 



these plasma corpuscles, at first freely swimming in the protoplasm, constitute a 

 phase of the fungus, the primary phase, wherein the fungus by its independent 

 appearance makes itself visible. The fungus has for weeks, months, possibly even 

 years, previously led a latent existence in an invisible form and alongside the pro- 

 toplasm of the host plant, forming a kind of mycoplasm-symbiosis between host and 

 parasite. 



Although Eriksson describes this mycoplasm in detail and figures it in 

 various stages of development, very few later writers have accepted his 

 evidence as being in any way conclusive. While it is not the present 

 purpose to give a detailed criticism of the theory, yet, in the judgment 

 of the writer, it seems that Eriksson's experimental evidence does not 

 establish his contention in regard to the existence of the so-called myco- 

 plasm. Nothing similar has been encountered in any of the hundreds of 

 sections which the writer has made. More will be said later of this 

 experimental evidence upon which Eriksson based his conclusions. 

 Ward (25, p. j^s) sums the matter up very well when he states that 

 Eriksson merely — 



inverts all the stages of the fungous attack on the cell, and supposes the last stage to 

 be the first and that this error and misrepresentation of the microscopic appearance 

 account for the whole wearisome persistence in an inherently improbable hypothesis. 



Detailed criticisms of Eriksson's theory are given by Bolley (4), Zukal 

 (26), Ward (25), and Massee (20). Others could be added to this list, 



