. The fungi which cause plant disease . Plant diseases; Fungi. THE FUNGI WHICH CAUSE PLANT DISEASE 239 On the leaves the first evidence of the spot is the slight blanching of a single one of the smaller areola of the leaf. Soon the blanch- ing extends to adjacent areolae, and if an areola is entered it is usually entirely involved. The small veinlets form the margin of the spot so that the outline is finely crenulate. By the time the spot is .3 to .4 mm. in diameter it has a cinereous appearance. The margin, while sharply defined, is not changed in color. By the time the spot is 1 mm. in diame
. The fungi which cause plant disease . Plant diseases; Fungi. THE FUNGI WHICH CAUSE PLANT DISEASE 239 On the leaves the first evidence of the spot is the slight blanching of a single one of the smaller areola of the leaf. Soon the blanch- ing extends to adjacent areolae, and if an areola is entered it is usually entirely involved. The small veinlets form the margin of the spot so that the outline is finely crenulate. By the time the spot is .3 to .4 mm. in diameter it has a cinereous appearance. The margin, while sharply defined, is not changed in color. By the time the spot is 1 mm. in diameter, the margin appears as a black line, while the remainder of the spot is grayish-brown. A i^ ®.SL. ^jy= Spates. FiQ. 174. Diagrammatic section through a pycnidium, show- ing how the spores are produced and how they germinate. After Reddick. little later the margin is a brownish band and the brown gradually extends inward until the whole spot is covered. As soon as the brown band attains some width the blackish line on the margin is to be seen again. A second wave of deeper brown may pass across the spot but sometimes it does not get entirely across and thus leaves a marginal band of a deeper brown than the central disc. Spots vary in size from 1 mm. up to 8 mm. in diameter, but in general are 3 to 5 mm. or larger. Occasionally the whole leaf is destroyed but this is by the coalescence of many spots. When the spot has attained full size pycnidia protrude from under the cuticle and either dot the entire surface of the spot with minute specks or are more often confined to a more or less concentric ring. The different shades of color are apparent on the imder side of. 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 Stevens, Frank Lincoln, 1871-1934. New York : Macmillan
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectfungi, bookyear1913
