304 MR. H. MARSHALL WARD ON THE 
From the faets that spores may remain dormant on the leaves 
during dry weather, and that they may retain their capacity for 
germination for several weeks if gathered dry and kept in cool, 
dry, sealed glass-tubes, the proof that moisture is necessary for 
their germination becomes strengthened; and this is, of course, 
in aecordance with what we know of other similar germinating 
bodies*. 
That oxygen is also necessary may be demonstrated: germi- 
nation is delayed or prevented if the spores be immersed in small 
air-tight chambers. Too low a temperature, as on flat open 
spaces, chilled by radiation to near the freezing-point, as well as 
artificially high temperature, kill the spores. Their rapid and 
vigorous germination at or near the temperature of 75? Fahr. is 
sufficiently established by numerous successful experiments. 
I demonstrated on several occasions the fact that the uredo- 
spore germinates well in the open on young vigorous coffee-leaves 
in the warm, damp atmosphere of the S. W. monsoon, and also 
showed that spores germinate under such conditions on the soil, 
in the meshes of exposed canvas-cloth, and on glass, &c.; whence 
it may safely be inferred that, given the conditions for germi- 
nation, any spore may throw out germinal tubes. If this occurs 
on the under surface of the coffee-leaf, the chances are infinitely 
in favour of the leaf becoming “infected” through its stomata. 
Complete infection may be taken to mean the successful 
establishment of the mycelium (derived from the germinal tube 
passing through the stoma) in the intercellular passage of the leaf. 
By cutting sections of the coffee-leaf at various periods after the 
spores were sown as above, it was shown that on or about the 
third day after the formation of the germinal tubes, the diver- 
tieula sent through the stomata were becoming established within 
the leaf as branching mycelial structures ; while further compa- 
risons demonstrated that during the second week after the sow- 
ing a well-branched and vigorous mycelium occupies that part of 
the leaf covered by the area on which the spores were sown. So 
constant are these phenomena that one could depend upon having 
preparations in a given stage for each three or four days after 
infection. 
From further observations it became clear that when the inter- 
* Nore added August 8th.—Spores of Hemileia, received by post from the 
Royal Garden, Kew, in July 1882, were successfully germinated in Strassburg 
on July 18-20th ; these specimens came from the island of Réunion. 
