Page:Proceedings of the Royal Society of London Vol 60.djvu/210

190 and that when freed from the oogonium it exerted an attraction on the antherozoids just like its larger sister oospheres.

When an oogonial nucleus is about to divide, it first becomes slightly, then very much, elongated so as to resemble an ellipse. Fine radiations are seen to extend from the two ends into the surrounding cytoplasm. The latter is at first tolerably uniformly granular, but as the radiations around the polar areas increase, these regions become cleared altogether of the granules which then become massed outside them. The nucleus rapidly becomes more spindleshaped, and its chromatic elements are chiefly grouped near each pole, leaving a clear space about the equator in which the nucleolus is situated. In this respect the nuclei of Fucus offer a striking contrast to those of Pellia epiphylla already described (‘Annals of Botany,’ vol. viii, p. 221) by one of us. In the latter plant the chromatic portion of the nucleus assumes an equatorial position at the corresponding stage in division, whilst the polar regions are clear.

The polar radiations continue to increase and the nucleus to lengthen, until the entire structure recalls the figure of a dumb-bell, in which the nucleus answers to the handle, and the radiation areas to the knobs. If the radii be traced outwardly, they are seen to terminate either in the frothy protoplasm, on the angles where the foam walls meet, or on the large granules which surround the cleared areas and are embedded in the foam. This point is one of considerable importance, and we shall revert to it further on. No structures were seen which could be identified as centrosomes, although bodies suggestive of them were often observed, but these proved to be so variable in size and position, as well as in number, that we feel unable to attach any special significance to them.

The next stage in the mitosis is that in which the interpolar spindle arises, with the chromosomes disposed upon its equator. The spindle is very remarkable inasmuch as it is entirely intranuclear, somewhat resembling that described by Fairchild for or 1\\ Harper for Peziza. The nuclear wall can be distinguished until quite late in karyokinesis, and it is possible that no complete mingling of the cytoplasm with the contents of the nucleus takes place here. The spindle is extremely clear, and in several preparations, owing to a fortunate contraction during manipulation, the ends of the nuclear part of the spindle also had broken away from the cytoplasmic poles, and were visible as clean conical structures forming the poles of the nuclear spindle. The chromosomes were too minute to admit of their development being satisfactorily studied, but in all the oogonial spindles their number was estimated at ten when seen arrayed on the spindle equator. They were only seen in profile, and consequently it was difficult to be sure whether there