144 ERIKSSON, MARSHALL WARD's RESEARCHES ON BROWN RUST. 



parent plant, as being in some cases the source of disease — 

 for one to be able any longer seriously to deny its existence. 

 It was in order to explain this mode of origin that I avan- 

 ced my hypothesis of a mycoplasm-symbiosis, and the ana- 

 tomical researches which I carried out for the purpose and 

 upon which I based that hypothesis had clearly then to be 

 carried out with such parts of plants — portions of leaves 

 and stalks — where the outbreak of pustules could 

 not be explained as a consequence of external infec- 

 tion by means of uredospores or aecidiospores. This exami- 

 nation must be carried out with parts of plants, which are 

 in the primary stadium of disease, a stadium w^hich 

 had been described in detail as early as 181)6^ and has been 

 distinguished from the secondary stadium which can be 

 wholly explained by the assumption that infection is of 

 external origin. 1 have, too, whenever 1 have afterwards 

 wished to assert the existence of an internal germ of 

 disease, always accentuated the fact that it was the fir fit 

 pustules of which 1 spoke, and by no means any manifestly 

 or, at any rate, presumably secondary ones that were 

 meant. 



To presuppose an internal germ of disease in a case 

 where infection by uredo- or aecidiospores has already taken 

 place, an infection which gives visible pustules after but 8 

 to 10 days, is unreasonable, just as it is incorrect to wish 

 to apply my way of explaining the origin of a primary 

 pustule fleck to the origin of a secondary one, or, upon the 

 ground of a histological examination of a secondary pustule 

 fleck to base a condemnation of a hypothesis which is appli- 

 cable to a primary pustule fleck alone. It is, however, 

 this mistake of which Marshall Ward now makes 

 himself guilty. On the basis of a histological examina- 

 tion of leave-flecks which had been artificially infected by 

 uredospores, he declares the mycoplasm hypothesis, i. e., the 

 entire theory of an internal germ of disease, to be erroneous 

 and »untenable». 



The mistake which has been committed is so much the 

 more surprising that it comes from so distinguished an in- 

 vestigator as Marshall Ward, and as I repeatedly warned 



^ J. Ebiksson k. E. Henning, Die Getreideroste, p. 189 etc. 



