Cell Proliferation in the Terminal Regions of the Internodes and Stolons of the Colonial Hydroid Campanularia flexuosa

Pattern formation and cell proliferation have been believedto have a causative relationship in the colonial hydroids. Herelinear stolon growth was assumed to be dependent on polarizedcell proliferation restricted to the extreme end of the stolon.The popularity of the concept that pattern formation was a resultof restricted meristematic cell proliferation was based on acorrespondence between the observed growth patterns and theconcept. Nevertheless, there is little direct knowledge of cellproliferation in the stolons of hydroids. The primary objective of this investigation was to determinethe sites of cell proliferation in the terminal growth zonesof the colonial hydroid Campanularia flexuosa in order to evaluatethis concept. The results give evidence that cell proliferationis more or less uniformly distributed throughout the terminalstolon and the internodes of upright stems, and not restrictedto the tips of the stolons and internodes as has been previouslypostulated. Cell proliferation occurs in both the epidermis and gastrodermisof the stolon in a ratio of 3 to 2. The formation of a new uprightis accompanied by increased cell proliferation localized atthe site of initiation. The uniform distribution of cell proliferation in the stolonsupports the hypothesis that growth is via intercalary cellproliferation, which was proposed eailier on the basis of evidenceobtained from the displacement of vital stained bands of tissuein the stolon. Stolon growth via intercalary cell proliferation requires areconsideration of the factors which control morphogenesis.Wolpert has pointed out the importance of determining the mitoticpattern in a developing system before an understanding of positionalinformation within the system may be studied. Thus, informationfor greater insight into the study of positional informationin a developing hydroid has been obtained.