THE MILLARDETIAN PERIOD 87 



biologic races or "special forms," as he called them, within 

 morphologic species of rusts.' This has been one of the 

 very fruitful discoveries in phytopathologic etiology 

 during the Millardetian period and has been extended 

 to other groups. Eriksson is widely known as the author 

 of the mycoplasm theory. This theory is one of the 

 most extraordinary and ingenious modifications of the 

 idea of symbiosis which any botanist has proposed. 

 The gist of the mycoplasm theory is that the naked 

 protoplasm of the pathogene lives for a time mingled in 

 indistinguishable combination with that of the host. 

 This mixed plasm Eriksson designates as mycoplasm. 

 He holds that at certain stages in the host's development 

 the pathogene protoplasm separates itself from that of 

 the host, migrates through the cell walls out into the 

 intercellular spaces, at first a naked nucleated mass not 

 unlike a Plasmodium. Gradually this takes on a thread- 

 like shape, secretes a cell wall, and sends haustoria into 

 the adjacent cells, and the pathogene mycelium is 

 formed. From this internal mycelium, present through- 

 out the plant, spore bodies arise beneath the epidermis 

 simultaneously. Thus he accounts for the sudden and 

 general outbreaks of rusts. The pathogene reverts to 

 the mycoplasmic condition in the next crop of seeds and 

 is thus perpetuated.^ Eriksson has persisted in main- 



' Eriksson, J. : Ueber die Specialisirung des Parasitismus bei den 

 Getreiderostpilzen, Ber. Deut. Bot. Ges., 12 : 292-331, 1894; also 

 Neue Untersuchungen iiber die Specialisirung, Verbreitung und Herkunft 

 des Schwartzrostes (Piiccinia graminis Pcrs.), Jahrb. Wiss. Bot., 29 : 499- 

 524, 1896. 



^Eriksson, J.: tjber die Mykoplasmatheorie, ihre Geschichte und 

 ihren Tagesstand, Biol. Centralbl., 30 : 618-623, 1910. (X concise 

 review of the matter with numerous references to the literature of the 

 subject.) 



