ARTIFICIAL CULTURES 63 
of a genus may have totally distinct rusts upon them, as in the 
genus Galiwm. So far there is nothing that would contravene 
one’s expectations, but it is impossible to avoid a little in- 
credulity when one is told that on Hieraciwm there is a 
Puccinia which is confined strictly to a single form of a variety 
of a subspecies of a species of that genus (Probst, 1909). 
These specialisations can be proved only by artificial cultures. 
Certain experimenters have developed very successful methods 
of infecting given plants with the spores. The ecidio- or uredo- 
spores are the handiest for this purpose. A sorus of mature 
uredospores is removed from the leaf, placed in a drop of water 
and broken up with a needle; the spores are then thoroughly 
shaken up with a suitable quantity of distilled water. The soil, 
in which the plant to be used is growing, should have been 
well watered before the experiment begins. The leaves to be 
inoculated are first sprayed with distilled water from an atomiser, 
and then the liquid containing the spores is similarly sprayed 
upon them, naturally upon a surface which possesses stomata. 
The plant is then placed under a bell-glass for 24—48 hours or 
longer, and afterwards kept in a greenhouse at a suitable tem- 
perature, protected if required by a larger glass shade with 
sufficient ventilation. A similar uninoculated plant should be 
kept near it asa control. In spraying, too great a quantity of 
moisture should be avoided; in nature it is observed that the 
germination of spores succeeds best in a layer of dew, not of 
rain. The keeping under a closed bell-glass is for the purpose 
of allowing the germ-tubes to enter the stomata; after that 
nothing more is required but to grow the plant in the ordinary 
way. The result of the infection will begin to appear in about 
10—20 days or more, according to the species. 
The inoculation with teleutospores which are ready to 
germinate may be effected in the same way; or a leaf with 
mature teleutospores may be tied, spores downwards, on the 
plant at the selected spot, and left to itself or protected for a 
time with a layer of wet cotton wool. If it be required to 
discriminate, under special circumstances, between the artificial 
infection and any accidental one that might occur, the leaf to 
be used may be marked with lines in waterproof ink, and the 
