140 ERIKSSON, MARSH ALL- ward's RESEARCHES ON BROWN RUST. 



species and groups of species of the genus Bromus. And I 

 acknowledge this all the more readily as the results given 

 agree very well with the observations I have myself made in 

 the cultures of a number of species of Brome.^ 



On the other hand, however unwilling I may be to dis- 

 agree with so distinguished an investigator as Marshall 

 Ward, I find myself compelled to question the accuracy of 

 the deductions made from these researches, concerning my 

 theory that an internal germ of disease is, in certain cases, 

 the source of rust.- The researches carried out have little or 

 nothing to do with that theory. The pure cultures in test- 

 tubes, described in 1902, where the results were negative in 

 the cases when no infective substance was introduced, prove 

 no more against the theory in question than do the nume- 

 rous experiments with cultures, equally negative in their 

 results, which I myself had carried out in isolated glass 

 houses during the years 1892 — 98.^ The negative results in 

 the tubes admit of precisely the same explanation as the 

 corresponding ones in the houses. Those instances again, 

 when disease appeared after infection in test-tubes, — in- 

 stances whose results correspond to those obtained by me in 

 an attempt at infection made August 23 — 24, 1892, in a glass 

 house* — merely show that artificial infection by means of 

 uredospores can give positive results even with plants kept 

 in the abnormal conditions inseparable from all isolated cul- 

 tures. 



I would not, however, have attached any especial im- 

 portance to the misleading deductions made by Marshall 

 Ward when he endeavours to find arguments in the results 

 of his researches against the theory of an internal germ of 

 disease, if these deductions had not, in consequence of the 

 investigator's great authority as a scientist, been re-echoed 

 in other countries,^ and if Marshall Ward, in a newly- 



^ J. Eriksson, Siir I'origine et la propagation de la Roicille des Cé- 

 reales par la Sentence. Ann. d. Sc. Nat., Bot.. Ser. 8. T. 14. 1901. Paris, 

 p. 107-112. 



^ J. Eriksson. Vie latente et plasmatique de certaines Urédinées. 

 Conipt. rend, de TAcad. d. Sc. Paris, 1897. p. 475. — Der heutige Stand der 

 Getreiderostfrage. Ber. d. D. Bot. Ges., Berlin. 1897, p. 193. — Sur I'o- 

 rigine etc., Ann. d. Sc. Nat., T. 15, 1902. p. 66 [Extr. p. 190]. 



^ J. Eriksson, Sur Vorigine etc., T. 15, p. 1-50 [Extr. p. 125 — 174]. 



* J. Eriksson. Sur Vorigine etc... T. 15, ]>. 7 [Extr. p. 131]. 



^ J. C. Arthur, Problems in the studg of Plant Rusts. Botanical 

 Society of America. Meet, at Washington, Dec. 31, 1902. Publication 22, p. 9. 



