The Parasitic Slime-Moulds.
31
losing its flagellum during the process, and then when once it is inside it becomes rounded or rather irregular in shape. It grows and may migrate further up the root-hair by amaboid movement. The swarm spore nucleus divides, and a small mutinucleated naked plasmodium is formed. Around each nucleus a wall is developed in a way similar to that occurring during spore formation. Each of these bodies is a zoosporangium and measures from 64-6.5p in diameter. The nucleus of the zoosporangium divides up into four or eight parts and around each a small mass of cytoplasm collects. The wall of the zoosporangium, which is quite thin, collapses, and the zoospores escape. Each zoospore is a spindle-shaped body 1-1.5 in length and from 0.5-0.7 in diameter. After escaping from the zoosporangium these zoospores fuse in pairs. This fusion may either take place in the root-hair or the individuals may migrate into the cells of the cortex and fusion may occur there.
in soil.
In hast time.
9
In cont
e
The Life-cycle of a typical member of the Plasmodiophoraceae.
a. Spore, b. emergence of swarm spore, . mature swarin spore, d. conjugation of swarm spores, e. un- inucleate amoeba, g. growth of plasmodium, h. stage of nuclear disorganisation prior to spore formation, j.-4. nuclear divisions prior to spore formation, I. a mass of mature spores. Stages .-. take place in the soil, de. in root-hairs, and J.-4. in the host tissue.
In all the other species where the infection stages have been followed, the swarm spores themselves fuse in pairs outside the host and a zygote swarm spore enters either through a root-hair or some other part and immediately makes its way into the parenchyma. Here it grows and may fragment into a number of parts or schizonts which migrate by amœboid motion and infect other neighbouring cells. These all develop into multi- nucleated amœba or plasmodia, see Text figure 1. It is only in Plasmodio- phora Brassicae that the formation of zoosporangia from the swarm spores, has been recorded.
Supplement No. 1, 1932.
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