The growth and morphology of two maize inbreds and their hybrid.

THIS INVESTIGATION lhad as its purpose the establishment of the nature and extent of the over-all growth differences and the morphological differences between two inbred lines of maize and their heterotic hybrid. It was designed to serve in part as the basis of studies of vascular system differences, and differences in phosphorus absorption and distribution in these same plants. These latter studies will be reported separately. MATERIALS AND METHODS.-The maize used consisted of two inbred lines bearing Universitv of Texas laboratory numbers 850 and 857, and the hybrid 850 X 857. Seed of both the inbreds and the hybrid were furnished by the Texas Agricultural Experiment Station, College Station, Texas. Before the plantings were made the weight of 100 air-dry seeds and of 50 embryos dissected from typical seeds was determined for each inbred and the hybrid. Seeds were planted in individual 2-in. pots of sand in the greenhouse on April 30, 1948. The hybrid seedlings emerged on May 3. Seedlings of 85.7 emerged on the following day, and these were followed 4 days later by a number of 850 seedlings. The hybrid seedlings nearly all emerged at the same time and they grew uniformly. The seedlings of 857 were only slightly less uniform and emergence of the whole planting was complete within 3 days from emergence of the first plant. The seedlings of 850 lacked the uniformity of the other two lines and emergence of the planiting required 6 days. Even so, it was not complete, for several 850 seeds failed to germinate. Ten days after emergence had begun, twenty-one plants of each line were selected on the basis of uniformity of size and appearance. These were "planted" in aerated culture solution in individual, glazed 1-gal. crocks provided with paraffined wood suipports. The culture solution contained, per liter: 1.5 millimoles of ammonium sulfate, 10 millimoles of calcium nitrate, 7.5 millimoles of magnesium sul1 Received for publication June 6, 1949. fate, and 2.7 millimoles of mono-potassium acid phosphate. This solution was supplemented with a "trace" element solution containing copper, boron, manganese, and zinc, and by iron as ferrous sulfate (Wolkoff, 1918; Hoagland and Snyder, 1933). Ten days after the plants were established in the culture solution (3 weeks after emergence), and at weekly intervals thereafter, individual plants, one of each inbred and one of the hybrid, were "harvested" for measurement. The following determinations were made on each plant: fresh weight of the root and the shoot, leaf number, length of leaf blade, width of the widest part of the leaf blade, length of the leaf sheath, length and diameter of the mid-section of each internode, and length of the ears and tassels, when these structures were present. RESULTS.-Seed and embryo weights for the inbreds and hybrid are given in table 1. The hvbrid seed averaged more than 25 mg. heavier than those of line 857 which were in turn about 24 mg. heavier than those of line 850. When the embryo weights were determined, however, it was found that the hybrid did not lhave any advantage, but that its embryos were intermediate between those of the two parents. Similar instances of hybrid vigor not related to a hybrid advantage in embryo weight have been discussed by, among others, East (1936) and Kempton and ,McLane (1942). Fig. I shows the weekly increase in total mass of the inbreds and the hybrid in terms of wet weight of the entire plant. Wet weight measurements were not made until the fourth week from planting on line 857 and the hvbrid, and the fifth week on line 850. By that time the hybrid had gained a considerable advantage in wet weight and it maintained this advantage throughout the experimental period. Line 857 which began with the heaviest embryo weight, but intermediate seed weight, maintained an intermediate position essentially throughout the entire experiment. These observations relative to the early development of the hybrid advan-