. A handbook of cryptogamic botany. Cryptogams. 328 FUNGI observed, however, and fertilisation takes place in the usual way. A very small quantity of gonoplasm (not visibly differentiated) passes over into the oosphere. The antherids and oogones arise together in this species, and develop in close connection. The oosperms form each a promycele, as described above. The sporangiophores of. Fig. 28S.—Simple sporophores of PhytophtJiora infestans de By. a, formation of fiist spores (zoosporanges) at ends of branches ; b^ two ripe spores on each branch and a third being formed {x about 200). (After
. A handbook of cryptogamic botany. Cryptogams. 328 FUNGI observed, however, and fertilisation takes place in the usual way. A very small quantity of gonoplasm (not visibly differentiated) passes over into the oosphere. The antherids and oogones arise together in this species, and develop in close connection. The oosperms form each a promycele, as described above. The sporangiophores of. Fig. 28S.—Simple sporophores of PhytophtJiora infestans de By. a, formation of fiist spores (zoosporanges) at ends of branches ; b^ two ripe spores on each branch and a third being formed {x about 200). (After de Bary.) Phytophthora, which resemble those of Peronospora in general habit, differ from them in the fact that each branch bears more than one pro- pagating body—not in chains, like Cystopus, but at intervals on the branch. In P. infestans a propagating cell is produced at the apex of each branch ; and as it ripens a papilla-like swelling arises beneath it ; the branch grows on and turns the cell aside. These propagat- ing cells are usually zoosporanges, but not unfrequently they are coni- diospores, differing from them in no other respect than the pro- duction of a germ-tube directly instead of zoospores. The zoo- ).—Zoasfar3n%esoi Phytophthora infestans spores are formed mthin and de By. a, division completed: b^ escape of zoo- ,. , ^ spores ; c. free zoospores; d, spores come to rest CSCapC QireCtly irOm the ZOOSpO- and germinating (x 390). (After de Bary.) ^^^^^ j^^^j^^ ^^ ^^ PcrOnOSpOra. Phytophthora infestans has a special economic interest, as the cause of the well-known potato-disease. The disease first appears, as a rule, on the green leaves of the potato plant in July or August, the sporangio- phores emerging through the stomates. Sporanges are formed, under favourable conditions of temperature, moisture, &c., in a few hours, are. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readabili
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