BONNER and DEVIRIAN (3) and BONNER (4) have shown that roots of different species vary appreciably as to the nutrients with which they must be'supplied for satisfactory growth in culture. ROBBINS (13) and WHALEY and LONG (15) have shown that roots of different lines of tomato differ particularly in vitamin requirements. The results do not make it clear as to whether the differences in response to added vitamins represent differences in ability of the roots 'to synthesize these substances for themselves or differences in ability to utilize the supplements. It can be anticipated, however, that if such differences exist among lines within a given species they may play some part in the development of general metabolic differences. It should be possible to study the inheritance patterns of these differences by utilization of root culture techniques in combination with a hybridization program to produce progeny in which these same characteristics can be investigated. The present study has been aimed at detecting the existence of line differences in roots of the tomato, Lycopersicon esculentum Mill. and related species with respect to the ability of the roots to synthesize and/or utilize thiamin, pyridoxine and niacin; at evaluating the significance of such differences; and ultimately at studying the inheritance of these differences.

The primary meristem is essentially the functional embryo of a plant. It remains undifferentiated, continually gives rise to new cells and is the ultimate source of all the organs of the plant. It has been studied for the most part in relation either to phyllotaxis or to the problem of germ layers. The significance of this meristem in the ontogeny of the plant has been stressed, but little attention has been given to ontogenetic changes within the meristem itself. Such changes obviously underlie its r6le in plant development. In an attempt to determine what changes take place in the apical meristem of the shoot during post-embryonic growth and their relation to growth of the plant as a whole, a series of developmental studies was made of these meristems in three species of tomato, Lycopersicon esculentum, L. racemigerum and L. pimpinellifolium.Methods.-Plants of each of the three species were grown under normal field conditions. At uniform intervals during development main stem tips of each type were killed and fixed. These, together with embryos from the seeds of each of these species, were imbedded in paraffin and cut into longitudinal serial sections, mounted and stained. The volume of the apical meristem, which for the purpose of these experiments is defined as that region at the stem tip in which the cells are meristematic, non-vacuolate and essentially isodiametric, was determined as follows: Projection drawings were made of each of the serial sections. These drawings were then placed upon wax plates of uniform thickness (determined by the thickness of the original sections and the magnification used) and cut out in the wax with a steel needle. Thus a wax model of each of the original sections was obtained. By weighing together those models corresponding to the series, of sections through each stem tip, multiplying the weight by the specific

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