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Avena flavescens Hordeum distichum 
Festuca elatior y murinum 
Bromus secalinus * secalinum 
»> mollis Lolium temulentum 
» arvensis 
CAN WHEAT MILDEW PROPAGATE ITSELF APART FROM 
THE BARBERRY ? 
If any botanist or agriculturist residing in Norfolk, or in the Fen district, were 
asked whether wheat ever became mildewed without the presence of the barberry, 
he would unhesitatingly answer in the affirmative, for the simple reason that we 
have the wheat mildewed to a greater or less extent every year, while the barberry 
is a very rare shrub with us. This is one of the strongest arguments used by those 
who oppose the theory of the hetercecism of Puccinia graminis, but apart from this 
consideration, it is of importance practically. Nothing seems more natural than 
to suppose the promycelium spores of Puccinia graminis should penetrate the leaf 
or stem of the wheat plant, through the epidermis, by their germ-tubes, and so 
give rise to the Uredo. But De Bary* distinctly says :—‘‘ The germination of the 
spores formed by the promycelium gave me previously the unexpected result that 
the germ-tubes donot bore through the epidermis of the host-plant. In various parts 
of Triticum repens, T. vulgaris, and Avena sativa, they remained as if they had 
been sown upon glass. The tubes turned irregularly in the most different directions, 
and died off quickly ; the grass plant on which they were sown remaining intact.’ 
It is obvious that De Bary is clearly decided in his own mind that these pro- 
mycelium spores do not penetrate the epidermis, not only of wheat, but also of 
twitch and oat plants. In my former paper on this subject,}+ two experiments are 
mentioned, one of which was unsuccessful ; but in the other, performed on April 
17th, 1882, five wheat plants were infected with freely germinating promycelium 
spores of P. graminis ; on April 24th the plants were uncovered, and on May 7th 
the true Uredo graminis appeared upon one plant. From the fact of these plants 
being exposed to accidental infection from the atmosphere from April 24th to May 
7th, a source of possible error is admitted, which considerably diminishes the 
value of this culture, for although this experiment was performed at a time of year 
when the spores of Uredo graminis and cidium berberidis were exceedingly 
unlikely to be blowing about in the atmosphere, yet my last year’s experience in 
Uredine culture impressed me very strongly with the extreme care necessary to 
exclude error from the entrance of foreign spores. Still, it must be remembered 
that the control plants were growing all the time this experiment was going on, in 
the open air in the same garden, and yet showed no traces of the fungus. This 
experiment was repeated later on in a more careful manner. On June 29th, four 
flower-pots were filled with earth, and had wheat planted in them. They were 
* De Bary, Neue Untersuchungen uber Uredineen, p. 24—25. 
t Plowright, Gardeners’ Chronicle, August 19, 1882, p. 223. 
