The Indeterminate Growth Factor in Tobacco and Its Effect upon Development.

A striking variation in agricultural varieties of tobacco (Nicotiana) has been frequently noted, in which the plants fail to complete vegetative growth and produce seed but go on growing in an indefinite manner until killed by frost in the fall. Varieties of tobacco commonly grown are characterized by a fairly constant average number of leaves. The new indeterminate-growth type produces a variable number of leaves according to the time of planting and length of season. Such plants have never been observed to flower in the field. When the plants are transplanted to the greenhouse at the end of the growing season they flower and produce seed during the winter months but the same plants kept alive and transplanted to the field the second year again fail to flower during the summer season. Plants started very early in the greenhouse and set in the field do not flower. Neither does restriction of growth by keeping the plants in small pots or pruning the roots favor seed production. GARNER and ALLARD (1920) have demonstrated that the blooming of this type of tobacco as well as of many other plants is governed by the relative length of daylight and sunlight. When the day is artificially shortened the new type of tobacco flowers and sets seed normally in the summer. The shortened day in the winter therefore is responsible for the change in the habit of growth when grown in the greenhouse. ALLARD (1919) has reviewed the occurrence of this aberrant form in many agricultural varieties. HAYES and BEIBHART (1914) report the appearance of indeterminate plants in the shade-grown Cuban tobacco in Connecticut. The original plants were found in the proportion of about one to a million. The variant has bred true to its type since that time and large numbers have been grown. It is one of the best examples on record of a mutation, as the change, although possibly a simple one, is visibly pronounced; the plants are sharply differentiated from the original stock and they were found in a naturally self-fertilized and uniform species and