1003.] On the Histology of Uredo dispersa, Erikss., etc. 353 



" On the Histology of Uredo dispersa, Erikss., and the ' Mycoplasm ' 

 Hypothesis." By H. Marshall Ward, Sc.D., F.B.S., Pro- 

 fessor of Botany in the University of Cambridge. Keceived 

 February 13,— Bead March 12, 1903. 



(Abstract.) 



The paper deals with a detailed study of the histological features of 

 the germination, infection, and growth of the mycelium of the Uredo 

 in the tissue of grasses. Primarily, the figures refer especially to the 

 Uredo of Puccinia dispersa in the tissues of Bromus secalinus, but com- 

 parisons are made with the behaviour of this and other Uredineae — 

 e.g., Puccinia glumarum and P. graminis — in the tissues of other grasses 

 and cereals. 



The research, which has been carried on over a year and a half and 

 has involved the preparation and microscopic examination of thousands 

 of sections, is principally based on the application of improved 

 hardening and staining methods to preparations from tube cultures of 

 the grasses concerned, the leaves of which were infected at definite 

 spots. These tube-cultures were prepared according to the method 

 previously described.* At definite intervals after sowing the spores — 

 e.g., after 1, 2, to 6 and 8 days — the infected areas were removed 

 and placed in fixing solutions, and the life-history of the fungus 

 traced step by step, and controlled by reference to uninfected areas. 



The full paper is illustrated by numerous figures, and deals with 

 the behaviour of the nuclei, vacuoles, septa, branches, haustoria, and 

 other details of the hyphae up to the commencement of spore- 

 formation. 



The relations of the hyphge and haustoria to the cell-contents of 

 the host are critically examined, and the cumulative evidence not only 

 fails to support Eriksson's Mycoplasm hypothesis ; but is completely 

 subversive of it, so far as histological facts are concerned. 



Eriksson's hypothesis, which refers the epidemic outbreaks of rust 

 to the sudden transformation into the mycelial form of a supposed 

 infective substance, previously latent and invisible in the cytoplasm of 

 the host, is shown to be untenable because the corpuscules speciaux of 

 this author are proved to be the cut-off haustoria of the fungus. 



Eriksson supposes that these corpuscules (haustoria) are formed by 

 the hitherto latent germs in the host-cells, growing up in the cells 

 into vesicles, which then pierce the cell-walls and give rise to hyphae 

 in the intercellular spaces. 



The present paper shows that Eriksson has entirely reversed the 



* " On Pure Cultures of a Uretline, Puccinia dispersa (Erikss.)" 'Roy. Soc. 

 Proc.,' 1902, vol. 69, p. 461. 



