LIBTNEAN SOCIETY OF LONDON. xliii 



and alternate generations each sort of reproductive organ buries 

 its germ in a different nutrient plant ; the vegetation of the 

 parasite is the sole cause of disease ; there is no pretence for 

 supposing that a morbid predisposition of the nutrient plant 

 causes or favours the attack of the parasite, but, on the contrary, 

 the more healthy a plant is, the more the parasite flourishes, if ex- 

 ternal conditions are favourable to it ; that the parasitic diseases 

 are contagious ; and that the observations tending to show pre- 

 disposition to attack have been made on perennial plants, and are 

 explained by the fact that the mycelium imbedded in these 

 plants is itself perennial. 



The observations of M. Oersted, of Copenhagen, translated in 

 the last part of the Journal of the Horticultural Society, are 

 directed to prove the identity of Podisoma Sabince (the tremelloid 

 fungus which grows on the branches of Juniperus Sahina) with 

 Moestelia cancellata (which attacks the leaves of pear-trees). His 

 experiments have satisfied him that the two fungi in question are 

 alternate generations of the same species ; and the author adds 

 that, from other experiments made by him upon JEcidmm Berhe- 

 ridis, he has arrived at the conclusion that JEcidium Berheridis 

 bears the same relation to Puccinia Graminis that Moestelia does 

 to Podisoma *. These observations are the more interesting from 

 the fact of their having been made by M, Oersted without any 

 knowledge of De Bary's investigations, which had contempo- 

 raneously led the latter writer to precisely the same conclusion 

 (as to ^ciditim Berheridis) as that arrived at by M, Oersted. 



De Bary's observations on the connexion between ^cidium 

 Berheridis and Puccinia Graminis are to be found in the Mo- 

 natsberichte of the Berlin Academy for January 1865. He has 

 carried out a series of careful experiments, which have satisfied 

 him that the sporidia of Puccinia Graminis germinate on the 

 leaves of Berheris, and that the JEciditcm of the Berheris is a 

 stage in the cycle of development of Puccinia. Thus, whilst 

 in most Uredinese the entire development is carried out upon 

 one and the same nutrient plant, the alternate generations 

 in Puccinia Graminis require a change of host. This (Dr. de 

 Bary observes) is a peculiarity to be especially remarked. It is 

 a state of things well known in the animal kingdom in the Taeniae 



* In the Reports of the Academy of Vienna, vol. li. p. 76, Keichardt de- 

 scribes as an ^^cidium a plant from New Zealand which (he considers) forms 

 an intermediate hnk between ^cidimn and Hoestelia. 



