I. Mahonia aquifolia as a nurse of the wheat mildew ( Puccinia graminis )

It has always been difficult to account for the widely-spread nature of outbreaks of wheat mildew in districts in which the common barberry is either entirely absent or very uncommon. In the year 1874 the Rev. James Stevenson found at Glamis, in Forfarshire, an Æcidium uponMahonia aquifolia , which the Rev. M. J. Berkelev pronounced to beÆcidium berberidis . In the following year Dr. Paul Magnus found the same fungus at Lichterfelde, near Berlin, but since that time it does not seem to have been noticed by any one. On the 31st of May, 1883, Mr. William C. Little, of Stagsholt, March, gave me a freshly gathered specimen ofMahonia aquifolia , upon the berries of which the Æcidium was abundant. Knowing that upon the barberry no less than three different AEcidia occur, I determined to prove by direct experimental culture whether this one was theÆeidium berberidis of Persoon (the æcidiospore ofPuccinia graminis ). At 10 p. m. on the evening of the 31st May I placed some of the spores upon the cuticle of some wheat-plants which had been cultivated under a bell-glass. In eleven days the uredo ofPuccinia graminis made its appearance upon these plants. The details of this, as well as of two other experiments, are appended. On the 13th June I placed some of the secidiospores upon a piece of wheat cuticle; in twelve hours they had germinated, and a little later the germ-tubes were seen entering the stomata, in the same manner as those ofÆcidium berberidis do (see figure). It is then clear that the Æcidium uponMahonia aquifolia is identical with theÆcidium berberidis (Pers.), and is a part of the life-cycle ofPuccinia graminis , and is unconnected with theÆcidium magellanicum (Berk.), and the Æcidium ofPuccinia berberidis (Mont.). The Mahonia in question is widely cultivated in gardens throughout England and is a favourite evergreen in shrubberies. It is also extensively planted in woods as a covert for game.