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Lectins were used as probes to investigate the mechanism of embryonic induction. Concanavalin (Con A) and gorse agglutinin out of 7 species of lectins tested were found to have strong neural-inducing effect on the presumptive ectoderm of newt gastrulae. Their effects were abolished by the addition of α-methyl-D-mannoside and α-L-fucose, respectively. Succinyl-Con A had a weak inducing activity in comparison to Con A. Autoradiography ofH-Con A-treated explants revealed that Con A bound to the inner surface, but not to the outer surface of ectoderm and was successively incorporated into cytoplasm.H-Thymidine incorporation was lower in the first half and higher in the second half of the 60 h cultivation period in Con A-treated explants as compared to controls.Con A-Sepharose had a strong inductive effect. This suggests that neural induction is caused through Con A binding to the plasma membrane, but not through incorporation into the cytoplasm of the ectoderm cells.

It has been reported that at the .outset of germination of Vigna sesquipedalis seeds the decrease in ribonucleic acid (RNA) content in a pair of cotyledons is precisely balanced with the increase in RNA in the seedling axis (plumules+ epi-and hypocotyls +radicle), whereas in the isolated cotyledons from the growing tissues no change in the RNA level takes place (Oota and Osawa, 1). On the other hand, in the hypocotyl at the middle of the germination stage (the definition of the germination stage has been given by Oota et al.) when the supply of cotyledonous reserves including RNA has nearly been exhavisted, net synthesis of protein ceases entirely to proceed and a marked drop In the RNA level occurs, and the drop is almost wholly recovered as a simultaneous sharp rise in the RNA level of the epicotyl (Oota et al.). In contrast to a considerable growth of the hypocotyl in the first half of the germination stage, no significant growth of the epicotyl initiates until the mid-germination stage, i.e., typical epigeal germination. If the epicotyl (together with the cotyledons and the plumules) is then removed, the RNA level of the hypocotyl is maintained almost unchanged thereafter throughout the latter half of the germination stage (Oota and Osawa, unpublished, cf. Oota). These facts appear to be hardly explainable without assuming ready migration of intact or nearly intact RNA molecules in the germ tissues in question.Participation of microsomal RNA in protein sj'iithesis is widely accepted. It is believed to be also the case for the bean hypocotyl where the rate of pro- Physiol. Plant., 12, 1950 [518]

The organization center of Cynopspyrrhogaster was divided into Parts 1, 2 and 3 of equal size (0.3 x 0.4 mm2) with presumptive fates as pharyngeal, pharyngeal+prechordal +trunk notochord, and trunk-tail notochord, respectively. Movements and changes in size and shape of each part were followed through gastrulation. Differentiation tendencies of each part were examined under three conditions: I, isolated; 11, sandwiched with presumptive ectoderm; 111, sandwiched with presumptive ectoderm after preculture in isolation for various times. In I, Parts 2 and 3 differentiated into dorsal mesoderm. In 11, each part induced dorsal mesoderm and neural tissues, the frequency being highest in Part 2 and lowest in Part 3. In 111, Parts 1 and 2 realized their presumptive fates, through changes in inductive capacities from trunk-tail to head. This change progressed rapidly in Part 1, and slowly in Part 2. Part 3 required induction by neighbouring Part 2 to realize its presumptive fate. Changes of inductive capacity of Parts 1 and 2 respectively, were chronologically similar in normal development and in preculture experiments. Lastly, the primary presumptive pharyngeal zone at blastula was proposed to act as an initiator of the organization center, its programmed information being transmitted to Part 2, and then to Part 3.The uninvaginated portion of the dorsal lip from early gastrulae organizes the trunk-tail (trunk or tail, or both) when transplanted or cultured in close contact with presumptive ectoderm from embryos of the same stage. The same portion acquires a head-organizing capacity after invagination or after a definite time of culture in isolation in Holtfreter's solution (1-6). These findings have been confirmed by others (7-10).Our results described above were unexpected, because the head organizer is located at the dorsal lip of the early gastrula (1 1). HAMA (12, 13) suggested that the motility of the organizer

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