Growth and Morphology of Tobacco Tissue Cultures In vitro

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Abstract
The growth in darkness of uniform cubes of two different sizes (6 and 17 mg.) of Nicotiana stem callus cultures on agar nutrient was studied during the course of 9 weeks. The histology of the growing cultures is discussed. Increase in size of cultures resulted from the proliferation of knob-like protuberances in which cell division was occurring very close to the surface. Though uniform in initial size and under constant cultural conditions, cultures grew at different relative rates, suggesting inherent differences in the initial culture pieces. Over and above the large amt. of variation in growth rate of cultures started from pieces of the same size (after 8 weeks, largest culture weighed 10 X smallest), there were also differences attributable to the initial size of the explant. The smaller the ex-plant the greater was the relative growth rate. For each series growth curves were plotted by reference to the largest culture at any time. In these terms the cultures increased exponentially with time for 5-6 weeks. Growth rates are described in terms of Blackman''s formula.