29 
host-plant he considers has been greatly over estimated. hee ey 
in 1875 thought 100 metres (120 yards) might be considered the ae 
but Eriksson puts it at from Io to 25 metres (12 to 30 yards). 3 
dissemination of the mildew in India, for instance, where the nearest 
Barberry is 300 miles away, on the Himalayas, cannot be effected by 
the ecidiospores. He found, too, that in Sweden the uredo on Triti- 
cum repens, beneath a Barberry-bush, sometimes appears before the 
zecidiospores on that bush ; or at any rate, before it had time to origin- 
ate fron the ecidiospores. Further, the teleutospores on P. graminis 
are capable of germination in spring only, and then only after they 
have been exposed to the vicissitudes of the previous winter, hence 
mildewed straw kept in a barn or in a stack Is not dangerous. 
Further, he finds that it is those teleutospores only which have been de- 
veloped in late autumn that are capable of germinating next spring. 
Let us recapitulate these statements :— 
1. That there are a multiplicity of different spore forms capable of 
affecting certain special host plants only, 
2. That the uredo and zcidiospores exhibit a certain degree of 
obstinacy and capriciousness in germination. 
3. The short distance they are capable of extending the fungus. 
4. The fact that the uredo has been observed before the zxcidios- 
pores, 
5. The limited germinative faculty of the teleutospores. 
Taking into consideration the above facts, it is improbable that the 
general dissemination of rust takes place in the usually accepted 
manner, viz., from separate centres and by geometric progression. 
In Sweden the dominant rust is Puccinia glumarum, and this form 
Eriksson has made the subject of special study, with the particular 
object of elucidating this question. In the first place he noticed that 
the uredospores in spring appeared on the young plants of certain 
varieties four or five weeks after the Wheat had been sown. and in 
the second place that sunniest parts of the fields were sometimes worse 
affected than the shady. ‘These observations induced him to try the 
following experiment : young plants immediately after the meltin 
of the snow in spring, were enclosed in wide glass tubes carefully 
packed at both ends with cotton-wool. In from six to eight weeks 
Uredo glumarum appeared upon them. It is possible that this may 
have resulted from an infection in autumn, although it is not probable 
for one would have ceteris paribus expected had this been the case 
that the uredo would have shown itself sooner, He therefore sowed 
