Survey of Anatomy, Ergastic Substances, and Nuclear Size in Echinocystis macrocarpa and Cucurbita pepo

Abstract

1. In Echinocystis macrocarpa the large differentiating vessels of the secondary xylem furnish excellent material for the study of giant nuclei. 2. The massive tuber is made up of storage parenchyma and a complex vascular network. Microscopically visible ergastic substances include abundant starch and a few small oil droplets. Immediate reaction with Millon's reagent indicates high protein. The core of the tuber is demarcated by amber color, lack of starch, and tissue shrinkage resulting in cleavage cracks. 3. Ergastic substances in the short-lived shoot are limited to rather abundant starch in the chlorenchyma of the outer cortex and in the sieve tubes and scattered starch grains and oil droplets in other tissues. High protein is indicated in sieve tubes and curiously also in the cell walls of collenchyma, pericycle, crushed phloem, and the xylem. Calcium oxalate is absent throughout practically the entire plant. 4. Structure and development of fruit and seed are outlined. Reaction is marked in the microscopically visible granular protein of the embryo cotyledons. 5. The differentiating vessels contain nuclei of relatively great size, the maximum 85 μ in diameter and 330,023 cu. μ in volume. This confirms the opinion expressed after the study of Ricinus that giant nuclei are of general occurrence in wide-vesseled plants. 6. The scale of nuclear growth is reckoned in comparison with the size of the meristem nuclei, 33 cu. μ = V. The cambial nuclei remain consistently small, 432 cu. μ = 13V, while the nuclei of hairs, collenchyma, and other vegetative tissues range from 4 to 187V. Endosperm nuclei measure 3,883V during early stages of growth. 7. Giant nuclei appear to be either in the resting or in the prophase condition. A surface network of chromatin is apparent. The nucleoli, one or more in number, are extremely variable in outline and contain minute, highly refractive droplets. 8. Shrinkage in volume, probably due to water loss, may result from sectioning. Nuclei in living parenchymatous cells when first mounted are outlined by encircling chloroplasts, translucent and therefore practically invisible. Their diameter is approximately twice that of nuclei in exactly similar closely adjacent nonliving cells. (A nonliving cell is here defined as one in which no trace of protoplasmic rotation or circulation can be detected.) 9. Contraction in volume is induced by dehydration of fresh material with absolute alcohol. The volume of free water ranges from 39 to 82 per cent. Actual increase in nuclear material is reckoned by comparison of the contracted nuclei with the meristem nuclear volume, V = 33, and amounts to 86-232 V. 10. The ratio of cell volume/nuclear volume in isolated typical cells from various tissues illustrates the variability of this figure (15:1 in meristem to 152:1 in vessels). 11. Cucurbita pepo is essentially similar to Echinocystis in the anatomy of the shoot. The nuclei in the developing vessels are somewhat smaller and reach a maximum of 66 μ and 163,643 cu. μ in diameter and volume. 12. Comparison of living material and prepared slides on both Echinocystis and Cucurbita indicates the necessity of the former in all studies pertaining to cell and nuclear growth.