In an earlier paper (7) the development of isolated heart-shaped and older embryos of Capsella4 (> 80 ,u long) when grown in a sterile nutrient medium containing mineral salts, vitamins and 2 % sucrose was described. It was also shown that supplementing the basal medium with a mixture of growth substances like indoleacetic acid (IAA), kinetin and adenine sulfate permitted development of still smaller globular embryos (40-80 ,u walking-stick-shaped (701-1000); inverted-U-shaped (1001-1700) and mature embryos (> 1700). For details see Raghavan and Torrey (7) and Rijven (10). taining 25 ml of the semi-solid medium. Cultures were kept in a culture room at 25 + 10 and given 12 hours illumination daily by a combination of cool white fluorescent tubes and incandescent bulbs giving about 50 ft-c light on the surface of the cultures (light-grown cultures) ; parallel sets of cultures were kept in an incubator which was completely dark except for brief periods of opening for examination (dark-grown cultures). Transfers to fresh media were made at intervals of 4 to 5 weeks.The morphogenetic changes occurring in the embryos were noted by periodic examination of the cultures. Growth measurements were made at the 2nd and 4th weeks from the start of the experiment, using a dissecting microscope equipped with an ocular micrometer. To get a clear picture of the effects of growth substances on the growth of the different organs in the embryos, the lengths of the cotyledons, hypocotyl and root were measured separately and their growth expressed in relative terms as the ratio final length/initial length. The root was operationally defined as the meristematic region at the proximal end and the primary root which subsequently developed from it, the cotyledons as the leafy structures at the apical notch of the embryos, and the hypocotyl as the region between the root and the cotyledons. The delimitation was arbitrary and difficult in early embryonic stages, but became easier in the later ones. Root length measurements did not include length of laterals.All experiments were repeated 2 to 3 times using embryos of various developmental stages. In any one treatment, embryos with initial lengths close to one another within 100 , were used. Although quantitative data on