CONTRIBUTIONS FROM THE WISLEY LABORATORY. 491 



Summary and Conclusions. 



The leaf-blotch disease of Iris (Heterosporium gracile) occurs on 

 many different species. The affected leaf fades much before the 

 normal time, and, quite apart from the unsightly appearance, it is 

 obvious that the shortening of the period during which photosynthesis 

 takes place is exceedingly harmful to a plant which stores up food 

 reserves for the next season's growth. The fungus can pass through 

 the winter in its fruiting form, and the spores are capable of germination 

 even after twenty-four degrees (F,) of frost. Also, as is usual with 

 many fungi, the other parts of the fungus are capable of regeneration, 

 and thus of forming a new centre for the spread of the disease. It 

 is obvious that all old leaves should be gathered and burned. A 

 dressing of slaked lime put on in autumn and lightly forked in in 

 spring has been found to be efficacious in eradicating the disease. 

 Further it would seem that the disease particularly affects lime-loving 

 species when the soil is deficient in lime, but not lime-hating species. 



The spores germinated in hanging drops of various substances, 

 and pure cultures were grown on preparations of agar-agar. 



Inoculations of living plants were successful, and showed that the 

 germ tube of the spore can pass through either the epidermis or stomata 

 of the host, and gives rise to mycehum which is both intercellular 

 and intracellular, but which does not possess haustoria. The fungus 

 completed its life cycle in these cases. 



An investigation of the previous accounts of the fungus has shown 

 that the attribution of the first description to Wallroth is incorrect, 

 his fungus being a species of Brachysporium. 



An attempt was made to inoculate Narcissus, as the fungus is said 

 to be the cause of a serious disease on the Continent. The attempt failed. 



Unfortunately, owing to leaving Wisley, I was unable to continue 

 the investigation as far as I should have wished. One of the points 

 which would probably have repaid attention was the unsuccessful 

 attempt to inoculate Narcissus. A large number of such attempts 

 would have shown whether the failure was due to the conditions not 

 having been the correct ones or whether other genera are immune to 

 the fungus from Iris. Is there a specialization of parasitism similar to 

 the one which is now so well known, particularly in the Uredinales, or 

 are there two different species which are very closely allied morpho- 

 logically and which have both been included in the same species ? 



In conclusion the writer wishes to express his sincerest thanks to 

 Mr. F. J. Chittenden, F.L.S., for suggesting this investigation, and 

 for his constant help ; to Mr. T. E. Rooney, of the National Physical 

 Laboratory, for photographs, except the slant culture, for which his 

 thanks are due to Mr. A. E. Malby, F.R.P.S. ; to Mr. W. R. Dykes, M. A., 

 Charterhouse, Godalming, for his kindness in answering certain queries ; 

 to Mr. R. J. Wallis for the hst of varieties affected by the disease ; 

 and to his brother, Mr. J. Ramsbottom, M.A., F.L.S., of the Natural 

 History Museum, for help in many ways. 



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