A. S. OUSTED ON PODISOMA SABIM. 



85 



full-grown and ready to germinate, upon the leaves of young pear- 

 trees, the leaves being placed under bell-glasses so as to keep 

 them in a moist atmosphere. On the 25th yellow spots were 

 already formed at the points where the mycelium had begun to 

 spread, and two or three days afterwards the first traces of sper- 

 mogouia appeared in the form of little transparent vesicles. The 

 number of these spermogonia continued to increase for several 

 days, and they have now almost all discharged their mucilaginous 

 spermatia. 



Thus we find amongst parasitic fungi relations which (so far as 

 regards the totally different aspect presented by the two genera- 

 tions and their entirely different habitat) are completely analogous 

 to those which exist in certain parasitic animals ; for the Podisoma 

 comports itself with regard to Roestelia precisely in the same 

 manner as Coenurus cerebralis (which attaches itself to the brain 

 of sheep and causes the staggers) does with regard to Taenia 

 scrrata, which infests the intestinal canal of the dog. 



In considering the result of this experiment in connexion with 

 those afforded by other experiments made by me upon JHcidium 

 Perberidis, the following conclusion is arrived at — that it must 

 now be considered as proved that JEcidium Perberidis bears the 

 same relation to Puccinia graminis that Roestelia does to Podisoma ; 

 or in other words, that the opinion entertained for a length of 

 time amongst cultivators that the parasitic fungus of the leaves 

 of the barberry is the true cause of rust in the Graminece is now 

 shown to be correct, and that, according to all appearances, this 

 disease in cereals will henceforth be preventible — a disease which , 

 in the time of the Roman Empire, caused such ravages that there 

 were temples consecrated to the god of rust (Eobigus) in which, 

 upon certain feast days, sacrifices were celebrated, and which 

 disease, in our days, has such an effect that here in Denmark it is 

 not unusual for the produce of the harvest to be diminished to 

 the extent of many millions of rix-thalers. 



As it may very easily happen that the above experiment may 

 be repeated many times without success, for those who are 

 occupied in this kind of work know that a certain amount of good 

 fortune is necessary for success. I have called in aid as witnesses 

 many of my scientific friends, amongst whom I may mention 

 MM. Japetus Steenstrup, Liitken, Th. Fries, Areschoug, Hoffman, 

 Dybdal, Th. Eotlie, &c. 



This notice had already been sent to press, when I learnt 



