GENETIC VARIATIONS IN THE MODE OF STOLON GROWTH IN THE HYDROID, CAMPANULARIA FLEXUOSA

Comparative observations of stolon elongation in 19 genetic stocks of C. flexuosa reveal four respects in which such activity may differ, with each varying independently of the others. Two of these determine the stolonic growth rate: the duration of the growth cycle and the average growth per cycle. The stocks show a nearly continuous spectrum of these values, ranging, respectively, from 6.05 to 7.18 minutes and from maxima of 8.8 to 26.5 µ. The resulting maximal daily growth of the stocks varies from 1.9 to 6.2 mm. This rate is influenced much more by the stolon's growth per cycle than by its cycle time. The stocks vary also in the frequency of their repeating pattern of retractions from cycle to cycle; this "trough period" ranges from 2.5 to 7. Thus indirectly it may be concluded that the duration of each cycle of back and forth hydroplasmic flow in the stolon is also an inter-stock variable. Finally, the stolons of many stocks show a secondary forward surge of the tip following shortly after time crest of the cycle is reached, and the frequency of such "secondary peak" formation is also a stock characteristic. Its anatomical basis is cited. With respect to these four parameters of stolon growth activity alone, 18 of the 19 stocks are distinct from one another. It is suggested that several of these traits are so constant and easily measured that studies into their mode of inheritance should be feasible.