Oogenesis and Fertilization in Albugo Ipomoeae-panduranae
Albitgo Ipomoeae-pandntranae (Schw.) Swingle occurs upon various species of Ipomoea, among others the sweet potato, upon which it inflicts, however, but slight damage. Its most common host is probably I. pandutrata, in which it induces great hypertrophy of leaves, stems, and flowers. The distortions are so marked as to attract the attention of even the casual observer. It is within these hypertrophied parts that the sexual organs and sexual spores are found in such abundance as to render this
... ecies the most favorable of all in the genus for the study of oogenesis and fertilization. The material is killed in admirable condition if cut in pieces a few millimeters square (the outer part being first shaved off to avoid endangering the knife by adhering sand) and dropped in chrom-acetic acid of the strength recommended for other species of Albugo.' The stain chiefly employed is the triple stain of Flemming. Inasmuch as several other species of Albugo have been described with considerable care, I will detail here only the more salient features, and those which present divergence from the usual types. The early history of oogenesis runs parallel with that of all other species of Albugo investigated; namely, the mycelium enlarges to form the oogonium, the nuclei enter, enlarge greatly, and pass to the spirem condition. This stage presents so little divergence from the same stage in other species that it is adequately represented by fig. 45 drawn from A. Bliti.2 Following the stage just described comes zonation or the differentiation of ooplasm from periplasm. In various species of Albugo zonation occurs in various ways. In A. Bliti the protoplasm condenses in masses which then run together to form the ooplasm.3 In A. Ipomocae-pandutranae zonation partakes more of the character exhibited in A. candida and A. Tragopogonis, in which the protoplasm may be said to fall away from the oogonial wall, leaving behind only a few strands, sufficient to suspend the oosphere in the center. This type of zonation is sufficiently illustrated by fig. 27 drawn from A. Tragopogonis.4 ISTEVENS, F. L., The compound oosphere of Albugo Bliti. BOT. GA7. 28: I49-176, 225-245. pls. II-15. I809. (P. 233). 2 STEVENS, F. L., loc. cit., pI. I2. 3 STEVENS, F. I., loc. cit., pI. 13, figs. 60-65. 4 STEVENS, F. L., Gametogenesis and fertilization irn Albugo. BOT. GA7. 32: 77-98, 157-i69, 238-26i. pbs-I-4. I90I-(p1. 3).