116 MASSACHUSETTS TIOKTICl LTUKAL SOCIETY. 



Some recent experiments in the culture of the Uredinese by 

 Eriksson, Klebahn, and others, show that some species of rusts 

 which are indistinguishable in form and which have quite a wide 

 range in parasitism, have become separated into biological forms, 

 the forms being confined to a narrow range of hosts in the number 

 of those ascribed to the species as a whole. For example, in 

 Puccinia graminis, the common wheat rust, which occurs on the 

 grains and many of the grasses, there are several form species, 

 which are shown to be quite certainly fixed, while there are 

 others which are not so certainly fixed. 



In Puccinia graminis three forms have been determined which 

 are considered fixed ; one form, secalis, on what might be called 

 the rye group, since it occurs on Secale cereale (rye) and also on 

 H'ordeum, pratense, Tr'iticMm. rej^ens, and Elymus arenarius ; a 

 second form, avena> on the oat group, Avena safiva, A. elatior,. 

 Milium effusum, Alojjecur'us j^^'ci't^nsis, and Dactylis gJoinerata ; 

 and a third form, aircn on a single species of grass, Aira cmspi- 

 tosa. Two other forms which are considered fixed have not been 

 certainly determined. They both occur on certain species of 

 grasses. Still another form occurs on wheat which is not con- 

 sidered fixed. 



These forms were determined by cross inocidations with uredo- 

 spores upon the different hosts, so that uredospores from any 

 member of the rye group would not infect any member of the 

 oat, aira, agrostis, or poa group, but would infect any member 

 ^f the rye group. Likewise, uredospores from any member of 

 the oat group would not infect any member of the other groups, 

 but would infect any member of the oat group. The wheat 

 form was found not to be fixed, since infection in a few instances 

 took place with uredospores from both the rye and oat groupu 

 This fact is looked upon as indicating that the form on wheat is 

 the original one from Avhich all the others have been evolved,, 

 and that it retains even at the present time some of its original 

 plasticity. 



Another interesting result of these investigations is the fact 

 that the puccinia spores from any of the groups can be used to 

 produce the lecidium, or cluster cup stage, on the barberry, but 

 the SBcidiospores from the barberry which were developed from 

 the rye group "would not work on the oat group, while tliey 

 would work on any niend)er of the rye group ; similarly tecidio- 



