180 
MR, H. MARSHALL WARD OH THE STRUCTURE 
meat. The resting-spore, at first simply a thin-walled dilation of the hypha, becomes 
separated by a septum, and its wall thickens gradually, bright granules and fat-like 
drops accumulating in the granular protoplasm. When quite mature, the protoplasmic 
contents assume a yellowish cast, but the thickened wall is only slightly yellow or 
colourless, perfectly smooth, and devoid of markings or mucilage, simply showing a 
slight tendency to stratification. It is not an uncommon event to meet with specimens 
like fig. 9, where one or two little branchlets arise close to the young spore and even 
appear closely applied to it (fig. 17); whether these are to be looked upon as repre¬ 
senting degraded pollinodial branches, or whether they are merely of the nature of the 
haustorium-like branchlets referred to before, I cannot decide ; it is quite certain that 
no fertilising tube is formed—the resting-spore arises purely asexually. The ripe spore 
exhibits a paler translucent spot in the centre, shining through the fatty and finely 
granular contents ; it is perfectly easy to convince one’s self of the attachment of the 
spore to the hypha in macerated specimens (figs. 10, 14, 19). 
It is an obvious question : On what does the proof that the resting-spores and the 
conidia belong to the same fungus rest ? The reply is simple and conclusive, though it 
has been by no means easy to obtain it. Putting aside the universal occurrence of the 
resting-spores in the white spots (fig. 1) as soon as they are well developed, and 
passing over the suggestive similarities to the “sporidia” of other Ustilagineae, shown 
in the germination of the conidia (fig. 25), there are two series of observations which, 
together with these, place the connection between the spores beyond doubt. 
In the first place the examination of very large numbers of careful sections has 
resulted in the obtaining of preparations like figs. 12-14, in which, although the 
anatomical continuity between a conidium and a resting-spore is not absolute, there 
can be no doubt as to the existence of that continuity. In fig. 14, the clearest case, 
the branch of the mycelium, passing up to the exterior, would end in a conidiophore, 
and it is attached to a branch bearing a resting-spore; and an examination of the 
other figure leads to the same conclusion ; the difficulty of laying bare the hypha 
along its whole course is, of course, immense. The conclusion of the proof of con¬ 
tinuity, however, is fully established by the production of the resting-spores from the 
conidia sown on the leaf. 
I have already mentioned that when the white spots are at their best they are 
covered with the numerous conidia as with an impalpable chalky powder; the resting- 
spores do not come to the outside, and thus it is perfectly feasible, and even very easy, 
to obtain pure sowings of the conidia by lightly passing a camel-hair pencil over the 
spots on an undamaged leaf. I have paid a great deal of attention to this matter of 
pure sowings and pure culture, and most of the clean sowings on glass {e.g., fig. 23) 
were obtained in this way : a clean, new camel-hair pencil was drawn lightly over a 
vigorous white spot, and a leaf infected in the manner described below, and then a 
glass slide was touched with the pencil, which still retained conidia; the purity of 
the last sowing was evidence of the purity of the infective sowing. 
