Towards the end of the summer the uredospores are replaced by
the winter resting-spores, called teleutospores, which are larger,
thicker-walled and darker in colour. These teleutospores remain
inactive on the straw until spring, when they germinate in manure
heaps or on moist ground and produce minute sporidia, which are
conveyed by air currents to the alternate host, in this case a barberry.
In due time the fungus, known as Aecidnim Berberidis, appears on
the barberry leaves in the form of small cluster-cups on aecidia,
each of which is filled with chains of orange-coloured aecidospores.
Infection of the leaves of the young wheat plants follows on the
scattering of the aecidiospores: a sorus of the rusty uredospores
is produced, and the life-cycle is complete.
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| Fig. 4.—Puccinia graminis. | ||||||||||||
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Though this is the normal and complete development of Puccinia graminis, it is not invariably followed. In Australia, for instance, the berberry is an imported plant and of rare occurrence, yet rust is very abundant. Teleutospores of heteroecious rusts never reinfect the host on which they are produced, so that in many cases the uredospores probably survive the winter in Europe as well as in Australia and give rise to the rust of the following year. Wind dispersal of the spores would account for mysterious appearances of the disease, in some years almost every straw in a wheat-field being affected, while in other years scarcely one is attacked. Rust disease does not directly affect the grains, but both quantity and quality are impaired by the exhausted condition of the wheat plants. No cure is possible, but as winter wheat suffers less than spring wheat, early sowing is recommended. Fungus spores will not germinate without moisture, and attention to drainage helps to keep down this and other fungus pests. It has also been observed that too heavy nitrogenous manuring stimulates and prolongs the growing period of the wheat; flowering is retarded, and thus there is a greater opportunity for infection to take place. Wheat growing on an old manure heap is nearly always badly diseased. Much attention has been paid recently to the cultivation of varieties of wheat that are immune to rust attacks, and care should be taken to select strains that have been proved able to resist the disease.
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From Vine's Students' Text-Book of Botany, by permission of Swan, Sonnenschein & Co. | ||||||
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Fig. 5.—Germinating Resting-Gonidia: A of Ustilago receptaculorum; B of Tilletia Caries (× 460). | ||||||
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The other two parasites, smut and bunt, affect principally the grain. Smut of wheat, Ustilago Tritici, infects the host at the time of flowering. The fungus-spores, from some diseased plant, alight on the stigma of the flower, and germinate there along with the pollen-grains. The developing seed thus encloses fungal hyphae, which remain dormant within the seed and in spring develop symbiotically with the growth of the wheat plant, doing no apparent injury until the time of fruiting is reached, when the fungus takes complete possession and fills the new seed with a mass of dark-coloured spores. These are scattered over the field and alight on other flowering wheat plants. It is impossible to detect the first infection or to cleanse the seed; the only remedy is to procure seed from a smut-free source, and to prevent further spread of the disease by gathering all smutted heads before the spores have matured or dispersed.
Tilletia Tritici, bunt or stinking smut of wheat, is so-called because the bunted grain has a disagreeable odour of stale herrings. Bread made from bunted flour is dark in colour, and both unpalatable and unwholesome. The spores of the fungus remain in the soil or in manure-heaps until spring, when they germinate and attack the first green leaves of the host plant. The after development is similar to that of smut, and the seed grain becomes a mere mass of fungus spores. Much can be done in this case to clean the seed before sowing by immersing it in hot water or in some solution that will kill the spores without injuring the grain.
Other parasitic fungi of less economic importance occasionally do considerable damage. Erysiple graminis, a mildew of grasses, has caused great loss in various countries; Dilophia graminis sometimes causes deformities of the leaves and inflorescence, another somewhat similar fungus, Ophiobolus graminis, attacks the leaves and stalks near the ground, completely destroying the plants.
Helminthosporium gramineum, a disease of barley, has also been recorded as growing on wheat; it forms long narrow dark-brown streaks on the leaves, which wither and die. The lower leaves are usually the only ones attacked, and the yield of grain has not been seriously affected.
WHEATEAR, a bird’s name, perhaps of doubtful meaning,[1] though J. Taylor, the “water poet” (d. 1654), in whose writings it seems first to occur, and F. Willughby, explain (in the words of J. Ray, the latter’s translator) as given “because [in] the time of wheat harvest they wax very fat.” The wheatear, Saxicola œnanthe, is one of the earliest migrants of its kind to return to its home, often reaching England at the end of February and almost always by the middle of March. The cock bird, with his bluish grey back and light buff breast, set off by black ear-coverts, wings, and part of the tail, is rendered still more conspicuous by his white rump as he takes short flights in front of those who disturb him, while his sprightly actions and gay song harmonize so well with his delicately-tinted plumage as to render him a welcome object to all who delight in free and open country. When alarmed both sexes have a sharp monosyllabic note that sounds like chat; and this has not only entered into some of the local names of this species and of its allies, but has caused all to be frequently spoken of as “chats.” The nest is constantly placed under ground; the bird takes advantage of the hole of some other animal, or the shelter of a clod in a fallow-field or a recess beneath a rock. A large amount of soft material is therein collected, and on them from 5 to 8 pale blue eggs are laid.
The wheatear has a very wide range throughout the Old World, extending in summer far within the Arctic Circle, from Norway to the Lena and Yana valleys, while it winters in Africa beyond the Equator and in India. But it also breeds regularly in Greenland and some parts of North America. Its reaching the former and the eastern coast of the latter, as well as the Bermudas, may possibly be explained by the drifting of individuals from Iceland; but far more interesting is the fact of its continued seasonal appearance in Alaska without ever showing itself in British Columbia or California, and
- ↑ The vulgar supposition of its being an euphemism of an Anglo-Saxon name (cf. Bennett’s ed. of White’s Nat. Hist. Selborne, p. 69, note) must be rejected until evidence that such ever existed be adduced. It is true that “whittaile” (cf. Dutch Witstaart and French Culblanc) is given by Cotgrave in 1611; but the older names, according to Turner, in 1544, of “clotburd” ( = clod-bird) and smatch ( = chat) do not favour the usual derivation. “Fallow-chat” is another old name still locally in use, as is “coney-chuck.”
