. Fungous diseases of plants : with chapters on physiology, culture methods and technique . Fungi in agriculture. PHYCOMYCETES 151. beak-like projections. The developing cushions break the epidermis and the mature spores are set free. Fig. 50, a, shows a section through a conidial cushion. Under favorable conditions germina- tion of the conidia proceeds promptly and each conidium becomes a zoosporangium, the protoplasmic contents dividing into six or more parts which emerge through an opening developed either ba- sally or terminally. The zoospores are set free as ovate swarm cells with two une
. Fungous diseases of plants : with chapters on physiology, culture methods and technique . Fungi in agriculture. PHYCOMYCETES 151. beak-like projections. The developing cushions break the epidermis and the mature spores are set free. Fig. 50, a, shows a section through a conidial cushion. Under favorable conditions germina- tion of the conidia proceeds promptly and each conidium becomes a zoosporangium, the protoplasmic contents dividing into six or more parts which emerge through an opening developed either ba- sally or terminally. The zoospores are set free as ovate swarm cells with two unequal lateral cilia. After a brief motile period they come to rest, become invested with a cell wall, and may push out a germ tube in a few hours. The oospores are normally, produced later than the conidia. The oogonia and antheridia de- velop in the intercellular spaces, and the mode of formation is Fig. 51. Fertilization in Cystopus much as in Pythium. The oogonia <After B- M- Davis» are, however, in this case larger, measuring from 50 to 60 p in diameter. There are numerous nuclei in the early stages. It is generally agreed that in this species the differentiation of the ooplasm is accompanied by a migration of the nuclei to a pe- ripheral position and the organization of a central body termed a ccenocentrum. A nucleus then returns from this nuclear zone to the region of the ccenocentrum. Preceding the latter, however, it is held that one karyokinetic division may be constantly found. The zone of the now disintegrating nuclei indicates fairly well the line of differentiation between periplasm and ooplasm. As the antheridial tube penetrates, a cell wall begins to be laid down be- tween ooplasm and periplasm. Into the tube of the antheridium a single antheridial nucleus migrates. Special attention is called to the fact that at maturity of the egg there is a single nucleus in each gamete, but the egg is also provided with a ccenocentrum. Fertilization proceeds exactly as in
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