The anatomical and physiological development of the Macrocystis sporophyte is examined from the undivided lamina stage until death. Spiral and alternate blade arrangements are both the result of nutation; blades are initiated in one plane. Sporophylls are seen as modified fronds. Haptera are negatively phototropic, and thigmotropism seems to stop their growth. Growth curves are used to define juvenility, maturity, and senescence phases. Growth of fronds, and perhaps of sporophylls is indeterminate, but growth of laminae is determinate. Plants live 4–8 years, fronds normally about 6 months. Canopy structure and blade arrangement are compared to forest canopies. Macrocystis does not readily recruit, and, especially M. integrifolia, relies more on vegetative propagation than on sexual reproduction to maintain itself. The growth of the plant is both environmentally and internally regulated. A brief review is given of known hormones in algae, and some areas of possible hormone action in Macrocyslis are discussed. Fertility is suggested to be controlled by some substance(s), left by the apical meristem in laminae which are to remain sterile. Prospects for future work are discussed.
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Christopher S. Lobban (1978) studied this question.