1
The Parasitic Slime-Moulds,
33
3. Spore-balls in sponge-like masses, irregular in outline, more or less solid but traversed by fissures, not enclosed in a common membrane. 4. Spongosporu. Page 36.
B. Spores not forming a spore-ball but associated in tetrads, which become broken up owing to absence of a common membrane.
5. Tetramyxa. Page 38. II. Plasmodium giving rise to both spores and zoospores.
4. Spores at maturity not arranged in a definite system, but
aggregated together; not enclosed in a common membrane.
6. Ligniera. Page 38.
Genus 1. Plasmodiophora Woron.
Woronin; Arb. d. St. Petersburg Naturf. Gesl. Vol. 8. Pp. 169-201,
1877.
Spores not aggregated together into a spore-ball, nor enclosed in a common membrane. Spores scattered irregularly in host cell. Plasmodia generally large frequently filling the cell. When mature, plasmodium gives rise to a large number of spores. On germination spores produce swarm spores which infect fresh host plants. The parasite produces hypertrophy of the host tissue.
The species included in this genus have recently been considered in detail by the author (1) and only a brief recapitulation will be made here. Only three species are recognised as belonging to the genus.
I.
P. Brassica Woron. (Pl. 13, fig. 1).
Woronin, M. Arb. d. St. Petersburg Naturf. Gesel. Vol. 8. Pp. 169-
201. 1877.
Woronin, M. Prings. Jahrb. f. Wiss. Bot.
Vol. II.
Pp. 548-574.
1878.
Spores spherical 1.6μ-4.3μ in diameter, with a
thin hyaline membrane which is not sculptured. Spores on germination give rise to swarm spores which infect the fresh plant. Swarm spores or swarm cells are uniflagellate 2.5-3.5 in diameter. After penetration they give rise, in the root hairs, to very small plasmodia or zoosporangia in which zoospores are produced. Zoospores are devoid of flagella, 1.5μ in diameter. Zoospores conjugate in pairs to produce plasmodium.
a
It
The organism causes hypertrophy of the roots of various wild and cultivated crucifers, particularly cabbage and other species of Brassica. occurs widely throughout the world, in temperate climates. In England it is known under the various names, Finger and Toc disease, Club root
(1) Cook, W. R. Ivimey and Schwartz, E. J.The life-history, cytology and method of infection of Plasmodiophora Brassicae Woron; the cause of Finger and Toe Disease of cabbages and other crucifers. Phil. Trans. Roy. Soc. Ser, B. Vol. 218 Pp. 183-314. 1930.
Supplement No. 1, 1932.
116