Sporogenesis in Nephrodium
common axis, but the poles of the spindle at metaphase hold their composite nature with entire absence of the focal center or centrosome. This account, which did much to dispose of the current idea that the development of the spindle in higher plants is controlled by centrosomes, is noteworthy. Then appeared two papers with detailed description of the method of division and distribution of chromosomes: one by CALKINS (I I) on Pleris tremula and Adiantum cuneatum; and the other by STEVENS (44)
... r by STEVENS (44) on Pteris aquiline, Cystopteris fragilis, and Scolopendrium vulgare. CALKINS believed that there was a tetrad formation of chromosomes in the prophase of the spore mother cell of ferns, and that the process of sporogenesis in those forms followed the same course as was observed in the maturation division of sexual cells in animals, with a transverse division and consequently a qualitative reduction in WEISMANN'S sense. STEVENS' studies on the forms named above disagree with CALKINS' view in several particulars, the main point being that there is present no transverse division of chromosomes in the spore mother cell, but two longitudinal divisions, and therefore there is merely a quantitative reduction. STEVENS' observation on the formation of daughter chromosomes in the second division was criticized by STRASBURGER (47). SMITH (42) investigated the sporogenesis of Osmunda regales. His results agree with those of OSTERHOUT in regard to the absence of centrosomes, and differ as to the origin and development of the spindle; he held that the spindle was bipolar from the beginning. In I904 GREGORY'S paper (26) was published. His account covers the sporogenesis of eight genera of ferns, i. e., Pteris, Scolopendrium, Asplenium, Onoclea, Davallia, Fadyenia, and two other forms among Cytheaceae, and seems to confirm FARMER and MOORE'S interpretation (i8) of the formation of chromosomes at the heterotypic division, indicating the occurrence of a transverse division. The next year STEVENS (46) published his results on the spore formation of Botrychium virginianum. His account begins with his so-called early prophase of the spore mother cell; the first appearance of the spindle of the first and second divisions, he finds, is within the nucleus. As regards the heterotypic mitosis, he states that the chromosomes in metaphase separate in the line of transverse fission This content downloaded from 080.082.077.083 on February 19, 2018 18:20:59 PM All use subject to University of Chicago Press Terms and Conditions (http://www.journals.uchicago.edu/t-and-c) 1908] YAMANOUCHI SPOROGENESIS IN NEPHRODIUM and that he agrees with the views maintained by FARMER and MOORE (i8), GREGORY (26), and STRASBURGER (49). CARDIFF'S (12) studies of synapsis and reduction in several forms of flowering plants and in Botrychium obliquum paid particular attention to the formation of the spirem and its behavior up to the formation of bivalent chromosomes in the heterotypic mitosis. According to him, paired threads, which appear in the presynaptic stage of the nucleus, fuse during synapsis and again split longitudinally after synapsis, probably along the line of the previous fusion. In I907 a paper entitled " Studies in apospory and apogamy in ferns" appeared under the joint authorship of FARMER and DIGBY (i6), whose two preliminary notes were published in I903 and I905. This paper deals directly with the matter indicated by the title, but some stages in the division of the spore mother cell are described in three forms of Lastrea and one species of Scolopendrium. The paper is accompanied by many important figures, but only three of the spore mother cells with heterotypic chromosomes are given, so far as sporogenesis is concerned. Recently there appeared two papers, one by BURLINGAME (IO) on Ophioglossales, and the other by GREGOIRE (24), with the title "La formation des gemini hete'rotypiques dans les vegetaux." BUR-LINGAME 's paper is chiefly devoted to a study of the sporangium. From the cytological standpoint GREGOIRE'S paper is very important. His views, which were published in I904 (25), concerning the structure of the resting nucleus of the spore mother cell, interpretation of synapsis, formation of chromosomes of the heterotypic mitosis, and distribution of the daughter chromosomes in the first and second divisions, were based chiefly upon BERGH'S studies (6, 7) of Allium, Lilium, and other forms; but in this recent paper GREGOIRE records the results of his own examination of Osmzunda regalis and four monocotyledons, which confirm his previous views. Nephrodium My present investigation of Nephrodium molle Desv. was carried on in order to understand the characteristics of the nuclear behavior of this species, and to obtain the knowledge prerequisite for a study of apogamy in the same species. Consequently this paper should This content downloaded from 080.082.