l82 
E. B. MAINS 
secondary and tertiary spores from the basidiospores of some rusts, 
but further development was prevented by contaminations present in 
his cultures. Carleton (1903) used different media and a substratum 
as nearly like a wheat leaf as possible and obtained only a little dif- 
ference in the length of the germ-tubes. Carleton, however, does not 
give an account of his methods. Ray (1901, 1903) has claimed to 
have cultivated a number of rusts upon decoctions of the host and on 
sterilized carrot and reports that in one case teleutospores were formed 
from the mycelium which was produced. Ray, however, gives only a 
very imperfect account of his methods. This coupled with the fact 
that he does not give either the species of rust or the kind of spores 
used subjects his results to criticism. 
The germination of rust spores has received considerable attention 
especially from later workers. Plowright (1889), Eriksson and Hen- 
ning (1894), Ward (1902&, 1903), Melhus (1912), Johnson (1912) and 
myself (191 5) have found that temperatures between 10° and 30° C. 
are necessary for good germination and that the optimum temperature 
is between 12 and 18° C. Fromme (191 3) has shown that a saturated 
atmosphere is necessary for abundant infection. 
The factors controlling the inoculation of the host after the germi- 
nation of the rust's spore have been principally investigated by Ward 
and his students. Miss Gibson (Ward, 1905) found that the germ- 
tubes of a number of rusts are able to penetrate into the inter- 
cellular spaces of plants other than their host without infecting. 
Furthermore Ward (1905) noticed this in the case of immune varieties 
of plants. He (19026) also observed that the germ- tubes of Puccinia 
dispersa had a tendency to be negatively heliotropic and suggested 
that this may be a factor aiding in inoculation. Robinson (1914) in 
the case of Puccinia Malvacearum and Fromme (191 5) and myself 
(191 5) in the case of Puccinia coronata have shown a similar reaction 
of the germ-tubes. Balls (1905) believes that inoculation is brought 
about by a hydrotropic stimulus which causes the germ-tube to enter 
the stoma of its host. 
The relation of the rusts to their host after infection has occupied 
the attention of a number of workers. De Bary (1887) and Jost (1907) 
have expressed the opinion that the predisposition of certain hosts 
for certain parasites is to be sought in the nature of the food which that 
host offers to them. De Bary (1887) and Tubeuf (1897) both have 
remarked that the rusts appear to adapt themselves to their host cells, 
