. Senescence and rejuvenescence. Age; Reproduction. 220 SENESCENCE AND REJUVENESCENCE. and growth beyond this size results in the formation of a new indi- vidual or individuals from some part of the old, that is, in some form of reproduction. The repetitive development in series of parts, such as node and internode, in the stem of the plant, of segments in segmented animals, and many other cases, are examples of similar relations between parts. The organic individual in fact exhibits a more or less definite sequence of events in space as well as in time, and it is impossible to doubt that a ph
. Senescence and rejuvenescence. Age; Reproduction. 220 SENESCENCE AND REJUVENESCENCE. and growth beyond this size results in the formation of a new indi- vidual or individuals from some part of the old, that is, in some form of reproduction. The repetitive development in series of parts, such as node and internode, in the stem of the plant, of segments in segmented animals, and many other cases, are examples of similar relations between parts. The organic individual in fact exhibits a more or less definite sequence of events in space as well as in time, and it is impossible to doubt that a physiological spatial factor of some sort is concerned. This problem has been considered at some length in an earher paper (Child, 'iia), and only brief mention of some of the important points is possible here. In the simpler cases of reproduction the spatial factor in dominance is clearly evident in the position of the part concerned in reproduc- tion with respect to the original dominant region. In Tubularia (Fig. 75, p. 211), for example, the stem and stolon increase in length, and when a certain length, varying with conditions which affect rate of metabolism, is attained, the tip of the stolon turns upward away from the sub- stratum and gives rise to a hydranth, as in Fig. 94. This hydranth and its stem grow in turn; a stolon arises from the base, and when a cer- tain length of stem plus stolon is reached, the process of reproduc- FlG. 94.—The primary form of agamic reproduction in Tubularia repeated. Evidently the stolon tip gives rise to a hydranth only when it has attained a certain distance from the original hydranth. The. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Child, Charles Manning, 1869-1954. Chicago, Ill. , The University of Chicago Press
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