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96 THE BRITISH SMUT FUNGI<br />

Spore germination. Spores germinate as soon as they are ripe at an optimum<br />

temperature of 13° to 22° C. (Walker & WeUman, 1926). Thaxter (1890) first<br />

observed germination. Anderson (1921) described fiow the promycelium remained<br />

short and hemispherical, while from it arose a whorl of branches which<br />

grew indefinitely to form myceUum. Older parts of the mycehum became empty,<br />

the protoplasm collecting in the growing tips. The cells tended to separate and<br />

detached fragments started new growth in culture. BHzzard (1926) confirmed<br />

these results. He described the promyceHum as a spherical vesicle about 6-10 /i<br />

diam. From it arose four to eight branches of variable length which continued<br />

growth and produced in 12 to 18 hours on onion decoction agar a dense weft of<br />

myceUum. Fusions were not observed and no sporidia developed. All cells of<br />

the hyphae developing from the promyceUum were uninucleate and remained so<br />

during the saprophytic life. Parasitic mycehum consisted at first of uninucleate<br />

cells but binucleate segments were seen in the young sorus, and before sporogenesis<br />

all the cells contained two nuclei.<br />

Infection of the host occurs through the cotyledon before the emergence of the<br />

first leaf at soil temperatures between 10° and 27° C. (Walker & Jones, 1921;<br />

Szembel, 1926). No resistant varieties of onion of commercial value are known<br />

but a fertile amphidiploid, obtained by crossing Allium cepa with the resistant<br />

species A. fistulosum, may be useful ,in breeding resistant types (Walker,<br />

Jones, & Clarke, 1944). The fungus survived in soil for 20 years (Moore, 1948).<br />

Urocystis colchici (Schlecht.) Rabenh.<br />

Caeoma colchici Schlechtendal, Linnaea, i, p. 241, 1826.<br />

Uredo colchici Link, Handbuch, iii, p. 435, 1883.<br />

Polycystis pompholygodes (Schlecht.) LeveUle, 1846 p.p.<br />

Polycystis colchici Tulasne, 1847.<br />

Urocystis colchici (Schlecht.) Rabenhorst, Fung. Eur., No. 396, 1861.<br />

Tuburcinia colchici (Schlecht.) Liro, 1922.<br />

Sori in the leaves as bhster-hke swellings parallel with the veins, 0-5-1-0 mm.<br />

wide, 2-10 or more mm. long, at first beneath the epidermis which later ruptures<br />

to expose the spores. Spore mass powdery, dark brown. Spore halls globose to<br />

irregular, 14-34 x 14-22 ju., each composed of one or two (rarely three or four)<br />

spores surrounded by a layer of yellowish, ovoid, sterile cells, 7-10 /x diam.<br />

Spores globose or angled to somewhat elongated, flattened on side of contact,<br />

reddish-brown, smooth, 12-16 /u. diam.<br />

On Colchicum autumnale. Also recorded on imported bulbs of Colchicum sp.<br />

and Bulbocodium vernum {Bull. Minist. Agric, Land., 79, p. 109, 1934).<br />

June. Wilts. Uncommon.<br />

Exsiccati: Berkeley, Brit. Fungi, 309 [as Uredo colchici^<br />

Spore germination. Unknown.<br />

Urocystis eranthidis (Passerini) Ainsworth & Sampson, comb. nov.<br />

Polycystis anemones var. eranthidiaVa.&serixxi, Erb. Critt. Ital., Ser. 2, No. 549,1871.<br />

Urocystis pompholygodes var. eranthidis (Pass.) Passerini, 1877.<br />

Tuburcinia eranthidis (Pass.) Liro, 1922 [as 'T. eranthis'].

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