. Comparative morphology of Fungi. Fungi. PERISPORIALES 193 rusts they belong to the few groups of obligate parasites which up to the present have resisted all attempts at culture on artificial substrates; as in the rusts, they do not kill the affected host tissue but may stimulate it to slight hypertrophies. The hyphae are strongly septate; their cells are uninucleate; the haustoria alone are sometimes multinucleate. Their walls are hyaline, except in Sphaerotheca mors-uvae where they become dark in age. As regards their behavior toward the host, they may be arranged in a noteworthy series fr
. Comparative morphology of Fungi. Fungi. PERISPORIALES 193 rusts they belong to the few groups of obligate parasites which up to the present have resisted all attempts at culture on artificial substrates; as in the rusts, they do not kill the affected host tissue but may stimulate it to slight hypertrophies. The hyphae are strongly septate; their cells are uninucleate; the haustoria alone are sometimes multinucleate. Their walls are hyaline, except in Sphaerotheca mors-uvae where they become dark in age. As regards their behavior toward the host, they may be arranged in a noteworthy series from endoparasitic, through hemiendophytic, to ecto- parasitic forms. Their lowest endoparasitic stage is represented by. Fig. 120.—Erysiphe Polygoni on Geranium maculatum. Development of haustoria. ( X 1,200; after G. Smith, 1900.) Leveillula taurica (Oidiopsis taurica). In it the mycelium lies, as in many parasites, in the intercellular spaces of the host leaves; only in the later stages of conidial formation do the hyphae emerge on the surface of the leaf and then form, like the other Erysiphaceae, an arachnoid or felty mat. These extramatrical hyphae cling by appressoria to the sur- face of the leaf; on this surface, however, they form no haustoria but nourish themselves, as do the hemiendophytic forms, by branches which penetrate the interior of the leaf through the stomata. In the hemiendophytic stage, as in Phyllactinia, the mycelium lives in the manner characteristic of mildews, extramatrically on the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Gäumann, Ernst Albert, 1893-1963; Dodge, Carroll William, 1895-. New York [etc. ] McGraw-Hill Book Company, Inc.
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