THE EFFECT OF SHAPE ON THE DEVELOPMENTAL AXIS OF THE FUCUS EGG

¹ From the Hopkins Marine Station and the Department of Biology, Stanford University

1. When recently fertilized eggs of Fucus furcatus are gently sucked into a small pipette while the cell wall is hardening, and are then blown out into sea water, an elongated shape is retained.

2. Elongated eggs reared in normal sea water at pH 7.8-8.2 form rhizoids at or near one end of the long axis. The axis of differentiation, as well as the plane of cell division, is thus determined by the shape imposed on the cell. The exactness of determination increases with greater elongation of the egg.

3. When Fucus eggs develop in sea water acidified to pH 6.0, they acquire a very strong tendency to form rhizoids toward the bottom of the culture dish (which blocks diffusion to form a gradient of products from the egg). This tendency largely overcomes the shape effect when elongated eggs are reared at pH 6.0, and most of them form rhizoids toward the bottom of the dish near the lower end of the vertical short axis.

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