SOME OBSERVATIONS ON THE EGGS OF FUCUS AND UPON THEIR MUTUAL INFLUENCE IN THE DETERMINATION OF THE DEVELOPMENTAL AXIS

¹ From the Laboratory of General Physiology, Harvard University, Cambridge, Mass.

1. The results of a number of observations and experiments are presented which relate to the nature of the Fucus egg and to some of the changes which take place in it at fertilization.

2. Giant eggs which in some cases develop supernumerary rhyzoids are found to originate in the fusion of single eggs within the capsule and especially at the time of emerging from the capsule.

3. The extent to which eggs fuse is found to be greatly reduced at low temperature and increased at high temperature.

4. Cross-fertilization between F. vesiculosus and Ascophyllum nodosum was found not to take place. The sperm of F. evenescens do not fertilize the eggs of F. veskilosus to any appreciable extent. Individual receptacles of the moncious F. evenescens are entirely self-fertile.

5. The developmental axis of the spores was found to be directed by the presence of nearby neighbors in F. vesiculosus, F. evenescens, and in Ascophyllum. The first division plane tends to lie so that the rhyzoid protrudes in the resultant direction of near neighbors. No jelly or other solid egg substance traverses the space between affected eggs.

6. Unfertilized resting eggs of another species were found to direct the division planes of eggs of F. evenescens equally well as dividing eggs of the same species. Therefore the directive effect cannot be ascribed to any agency dependent on nuclear or cell division in the directing cells.