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^^ THE BBITISH SMUT FUNGI
Young healthy mycelium is full of granular protoplasm with an affinity for
stains, such as gentian violet, saffranin, and fast green, but in older tissue
portions of the mycelium may be empty and coUapsed, sometimes having the
form of a long filiform strand, sometimes thick with an enveloping sheath
(Kolk, 1930; Woolman, 1930; Western, 1936 b; Evans, 1933). It is not always
easy to find mycehum in older plants, but it does not disappear entirely, and
sometimes sporulation occurs in late tillers induced to develop by removing
those first formed and smut-free.
Some smuts which attack perennial plants are systemic, hibernating in underground
stems or bulbs and reappearing each year to form spores in the appropriate
part of the host. Mycelium of Ustilago vaillantii, for example, can be
found at the base of bulbs of the grape hyacinth, where the mycelium forms
botryform haustoria, consisting of a cluster of short inflated branches. Each
year mycelium passes into the young inflorescence and sporulates in the anthers,
replacing the pale yellow pollen by dark chlamydospores but having otherwise
little effect on the host (Massee, 1914). De Bary recorded a plant of Saponaria
officinalis in the Freiburg Botanic Garden, which was for ten successive years
affected with U. violacea, and Plowright refers to plants in his garden at King's
Lynn of Golchicum autumnale, Agropyron repens, and Arrhenatherum elatius
which carried their respective smuts for at least six years (Plowright, 1889).
Among the perennial economic grasses infected by a smut mention may be
made of timothy and smooth-stalked meadow grass, which are sometimes
severely injured by stripe smut (Davis, 1926; Kreitlow & Myers, 1944). ^
In some smut diseases the area of infection is localized, the fungus sporulating
not far from the seat of invasion. U. maydis, for example, which attacks
axiUary buds or young floral organs, produces in a comparatively short time
small or large swellings containing spores. Each gall or ball usually represents
a separate infection. Species of Entyloma, which attack the leaves of many
different plants, form angular Ibsions, the chlamydospores developing round
each infection centre in a typical leaf spot, except where very heavy infection
destroys the whole lamina.
Before emergence of the ear it is not possible to distinguish with certainty
in the field plants of wheat, oats, or barley systemicly infected by smuts, but
careful records and measurements have shown that the growth of the host is
affected in several ways. Oat plants carrying smut produce extra tUlers, while
growth in height is often considerably reduced (Talieff & Grigorovitch, 1923;
Sampson, 1929; Welsh, 1932). Even smut-resistant varieties may be adversely
affected in growth and vigour (Hubbard & Stanton, 1934; Stevens, 1936).
Bunt of wheat may either promote or retard tillering but it almost" invariably
reduces height (Zade, 1931; Lang, 1917a; Mourashkinsky, 1925; Viennot-
Bourgin, 1937), the magnitude of the effect depending on the variety and the
physiologic race of the fungus (Holton, 1935; Aamodt e( aL, 1936; Schlehuber,
1937). The effect of bunt on the form of the wheat ear also varies. A broadawned
ear like that of American Club (Triticnim compactum), if bunted, is
abnormally long and awnless; a lax ear, like that of Hen Gymro (T. vulgare),
when attacked by bunt is shorter and the awns are also reduced in length
(Sampson & Davies, 1927; DiUon Weston, 1929). Wheat plants infected by
U. nuda are said to be markedly stunted and their dry weight at flowering time