In vitro studies on the embryo of Capsella bursa-pastoris

1. The distinction between pregerminal and postgerminal embryo culture has been defined and emphasized. The literature on the former has been surveyed from a physiological point of view. 2. Chapter II gives an account of the development of the embryo of Capsella in ovulo. The embryogenesis was divided in stages. The formula of the sigmoid growth curve could be determined by means of a graphical treatment of the data. Chemical and physico-chemical properties of the embryo and the endosperm were studied; the pH of the latter is 6.0 and the osmotic value is isotonic with 3/8 mol mannitol (8.4 atm). The osmotic value refers to ovules with “torpedoes.” 3. Chapter III reports methods of and results with pregerminal embryo cultures. a Culture cells were used for the cultivation of embryos, that were suspended in drops between two glasses so as to enable the observation of 25 embryos per vial. The growth was measured by a microscope with an ocular-micrometer. b. In preliminary experiments on torpedoes (0.5 mm) the influence of some general conditions (pH, temperature and light) was examined. c. Sucrose proved to be a superior source of carbon. d. Casein-hydrolysate favoured the growth strongly. e. A concentration series of a complete amino acid mixture verified that amino acids are limiting growth. f. Ammonium lactate could not substitute amino acids as a food factor. g. In cultures of heart-shaped embryos glutamine gave better growth than a nitrogen aequivalent, complete amino acid mixture. In this respect glutamine proved to be exceptional and outstanding among the amino acids tried. h. In contrast with glutamine, asparagine gave extremely low growth values, but in the embryos an abnormally rapid and strong starch production was observed. i. Experiments on the influence of bios factors and purine derivatives gave negative results. Indole-3-acetic acid had a real, though small influence: it stimulated growth in a concentration of 0.001 p.p.m. and inhibited it in concentrations up from 1 p.p.m.. 4. Chapter IV demonstrated the viability of cultivated embryos by means of postgerminal cultures. Germination appeared, when the osmotic value of the medium was lowered. 5. In the discussion the results of the cultures are confronted with the embryogenesis in ovulo and with the data of the literature. I should like to express my appreciation to Prof. Dr V. J. Koningsberger, Department of Botany of the State University, Utrecht, who suggested the problem, for his interest and his kind help in preparing this paper for the press. I should also like to thank Mrs. M. A. Rijven-Simons for her constant technical assistance and for translating the manuscript.