Versuche zur somatischen Beeinflussung der Organbildung pflanzlicher Embryonen
Experiments on influencing cotyledon formation in embryos ofEranthis hiemalis are reported. By treating the seeds with 100–2000 ppm solutions of 2,4-dichlorophenoxyacetic acid, 2,4,5-trichlorophenoxyacetic acid, 2-methyl-4-chlorophenoxyacetic acid, α-naphthylacetic acid and even isopropyl N-phenyl carbamate one can obtain significant increases in twinning and in cotyledon anomalies (syncotyly and pleiocotyly of all degrees). Embryos can be successfully treated until approximately 2 weeks after initial opening of the follicles. X-radiations achieve the same effect, with doses of 2000–4000r corresponding to the treatments with 1000–2000 ppm 2,4-D-solutions. By using weaker concentrations and with sudden temperature changes one can likewise raise the percentage of syn-, tri- and tetracotyls, but pleiocotyls of the higher degrees (5 and more cotyledons) appear only when more intensive methods of treatment are employed. These forms which exceed the normal range of variability arise as bud-like embryo regenerates on the as yet undifferentiated original embryo.
CULTIVATION IN VITRO OF SMALL DATURA EMBRYOS
WHILE ATTEMPTING to induce artificial parthenogenesis by inj ecting physiologically active substances into unfertilized ovaries of Datura stramonium (16) it was realized that some of these substances might never penetrate the ovules far enough to reach the egg cell. With this in mind experiments were planned by which the development of the egg cell and the subsequent parthenogenetic embryo, should such be obtained, could take place in vitro. In order to accomplish this, two major steps are necessary: (a) division of the egg cell must be induced, and (b) development of the resulting embryo into a viable plant must be accomplished. It seemed obvious to try to control step (b) before attempting (a). The present paper deals with step (b), the culture of small embryos in vitro. Successful culture of embryos has been reported in the literature (10, 14, 20). For a review of the literature, see LaRue (10) and White (19). The media used by the different authors vary considerably. Tukey (14) concluded that there was no appreciable difference in effect between the different salt solutions used by various workers. The concentration, too, could be varied from one to ten times without much effect. It seems clear, however, that the necessity of adding organic substances to the medium greatly depends upon the stage at which the embryos are isolated. Thus mature embryos can be grown in a strictly inorganic medium. The addition of sugar even retards their growth (14). Nearly mature embryos require sugar (10, 14). According to Tukey, the younger stages require more than the older ones. Still younger embryos require, in addition to sugar, the heat stable factors found in yeast extract or fibrin digest (10, 20). LaRue employed indoleacetic acid in low concentrations to replace yeast extract in his media. Although the embryos successfully cultured by the authors mentioned above were often very immature, they still were isolated at a relatively advanced stage of development. LaRue (10), who successfully grew the embryos of a large number of species, makes the following statement: ". . . embryos 0.5 mm. or slightly less in length can be grown successfully . . . those of still smaller size have not yet been brought under control. . . . at a length of 0.5 mm. we may have reached a new lower threshold which will be difficult to pass." It is well to remember that the actual size of an embryo is not a measure of the stage of development in different species. Thus an embryo 0.5 mm. long of a plant having relatively large embryos, such as Datura, will be in a much earlier stage of development than an embryo of the same length of a plant such as Nicotiana, which has minute embryos. White (20) isolated young heart-shaped embryos from Portulaca. These embryos grew from 0.12 to
Über die postgenitale Verwachsung in Karpellen
Es wurden postgenitale Verwachsungen an oberständigen, apokarpen, latent peltaten und epeltaten Karpellen aus den Familien der Magnoliaceae, Calycanthaceae, Ranunculaceae, Crassulaceae, Rosaceae, Leguminosae, Asclepiadaceae und Alismataceae an 140 Arten untersucht. Es handelt sich in allen Fällen um Verwachsung, im Unterschied zu bloßer Kutikularverzahnung. Verwachsung entsteht durch Wachstum, oft unter periklinalen Teilungen, der Epidermiszellen, bevor sie eine mit den gewöhnlichen Methoden nachweisbare Kutikula gebildet haben. Die Verwachsungslinie bleibt entweder bis zur Ausbildung der Trennungsgewebe der Frucht deutlich sichtbar (Magnoliaceae, Calycanthaceae, Ranunculaceae, Alismataceae) oder sie ist schon lange vor der Blütezeit völlig unkenntlich (Papilionatae, Asclepiadaceae) oder sie verhält sich intermediär (Crassulaceae, Rosaceae, Mimosoideae, Caesalpinioideae, Sophoreae, schließfrüchtige Ranunculaceae-Karpelle). Das verschiedene endgültige Aussehen kommt dadurch zustande, daß verschieden alte Stadien des Verwachsungsvorganges als Endzustände erhalten bleiben. Früher Verwachsungsbeginn macht ein Durchlaufen des gesamten Vorganges möglich, bei spätem Beginn werden nur die ersten Stadien, die sonst Durchgangsstadien sind, erreicht und als endgültige Zustände festgehalten. Der Grad der Verwachsung ist — abgesehen von den schließfrüchtigen Ranunculaceae — unabhängig von der Öffnungsweise der Frucht, steht aber anscheinend in Beziehung zur phylogenetischen Höhe.