On wheat mildew (Puccinia graminis, Pers.) and its connection with the barberry aecidium (Ae. berberidis, Gmel.) / by Charles B. Plowright.

  • Plowright, Charles Bagge, 1849-1910.
Date:
1882
Catalogue details

Licence: Public Domain Mark

Credit: On wheat mildew (Puccinia graminis, Pers.) and its connection with the barberry aecidium (Ae. berberidis, Gmel.) / by Charles B. Plowright. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    pieces, and laid flat upon the earth, so that as soon as the young Wheat plants appeared above the surface they came into direct contact with it. Some light will also be thrown upon this subject by the investigation of the other heteroecismal Puccinia. P. rubigo vera has this year been extremely abund- ant ; hardly a specimen of Holchus lanatus exists in this neighbourhood without harbouring it. But the iridium which occurs on various Boraginacese I have never been able to find. This Puccinia recurs year after year on the same plants of Holchus, with no Boraginaceous plant in the vicinity. Again, only yesterday I walked over some pasture land not very long reclaimed from the sea on which Puccinia coronata in both the Uredo and Teleutospore state occurred in the greatest profusion ; and to my certain knowledge there is no shrub of either Rhamnus frangula nor cathartica within 4 miles. All this points to but one conclusion, namely, that the heteroecismal Puccinise can propagate themselves without the inter- vention of their ^Ecidia. The heteroecismal Pucciniae at present known are all found either upon grasses or carices. In this county they are seven in number, namely, P. graminis, with its ^Ticidium on Barberry ; P. rubigo vera, with its HLcidium on Boraginacese ; P. coronata, with its Aicidium on Rhamnus frangula and cathartica; P. Moliniae, with its ^Ecidium on Orchis latifolia, &c.; P. poarum, with its /Ecidium on Tussilago farfara ; P. caricis, with its ^Ecidium on Urtica dioica; P. sylvatica, with its .^Ecidium on Taraxacum officinale. As the ^Ecidium state is known to be the product of the promycelium spores, one is led to consider whether there be anything in the structure of the grasses and carices inimical to the entrance of the germ-tubes of these spores. In the passage already quoted from De Bary he speaks of the germ-tubes of the promy- celium spores not boring through the epidermis, and suggestively adds that “ they remained as if they had been sown upon glass.” Here I believe lies the explanation, these germ tubes do not bore through the epidermis because they cannot. The amount of silica in the Graminse is well known, and has been spoken of as “ Nature’s waterproof mantle ; ” it may with equal truth be said to be “ Nature’s spore- proof mantle.” The germ-tubes of the promycelium spores, it will be remembered, are very diminutive structures compared to most of the Uredo and yEcidium spores. They are not long enough to travel over the surface of the blade and search for the stomata as those of the latter spore-forms do. The last-named germ-tubes do veritably search for the stomata. The main tube almost always travels across the blade at right angles to its long axis, sending off here and there short rectangular branches when it passes over the junction of two cells, as is shown in figures in my previous paper.* Of course the minute germ-tube of the promycelium spores is quite inadequate to do this. There is no reason, however, why these germ- tubes should not enter any part of the Wheat plant that is not armour-plated. In the two experiments just mentioned, in which Wheat plants grown under glass were so placed that their plumules came in contact with the teleutospores of P. graminis as soon as they came above-ground, became infected with the fungus, while the control plant remained healthy. That this is by no means an impossible suggestion is shown by the analogous case of Cystopus candidus, in which De Bary found the plants became infected with the fungus through the entrance of the zoospore germ-tubes into the cotyledons. But we are not con- fined to the plumule as the only vulnerable point ; the rootlets may be points of entrance. Considering how constantly stray Wheat plants growing upon manure heaps are affected with mildew, this mode of entrance does not seem at all improbable under those conditions. The roots and root-stock of the Wheat plant are more likely to be in contact with the germinating teleutospores than when the plant is grown in the ground. The fact, too, of perennial grasses being annually the hosts of various heterce- cismal Puccinise would also seem to indicate the possibility of the plants being infected through some other channel than the plumule. These points are, however, at present only suggestions, which I hope to put to the proof next spring. Charles B. Plowright, Kings Lynn. * See p. 6, fig. 1,0; p. 9, fig. 3, i. ERADBURY, AGNEW, & CO., PRINTERS, WHITEERIAR5.
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