POTENTIALLY UNLIMITED GROWTH OF EXCISED TOMATO ROOT TIPS IN A LIQUID MEDIUM

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Abstract
Tomato root tips, excised, and grown in a simple liquid medium of known constitution, have been maintained for over a year, and through 52 passages, in continuous active growth as measured by increase in number of growing points and total volume of tissue. One isolation has produced in vitro approximately 35,000 growing points and more than 400,000 mm. of tissue, from an initial fragment 10 mm. long. Calculations based on averages from approx. 40,000 separate observations on this clone give the theoretical dilution of any material of the original fragment as well beyond 10-40, hence beyond the limits of molecular dilution. The entire material of most, if not all, of the ultimate cultures is therefore necessarily derived from the nutrient. This nutrient is thus demonstrated to be adequate for all growth requirements of such tissue. The growth rates have shown no consistent tendency to fall off, there being, on the contrary, a consistent increase in the early passages from 1.5 mm. per culture per day in the 1st to 6.8 mm. in the 26th passage, the corresponding value at the 52d passage being also 6.8 mm. per culture per day.