Page:Proceedings of the Royal Society of London Vol 60.djvu/212

192 cytoplasm also changes, and tends to assume a more definitely radiating character, the lines starting from the nucleus as a centre.

We observed, not unfrequently, rather large cells in which twonuclei of equal size were lying in close juxtaposition. These cells, with their nuclei, answer exactly to the description given by Behrens of the fertilisation stage in plants examined by him. We are unable however, to accept his interpretation, for, in the first place, the series of fertilisation stages which we have observed, and have briefly described above, in no way correspond with the appearances described by him, and secondly, because these large cells (Behrens himself emphasises their size) are seen in material to which no antherozoids have had access. Furthermore, the average size of the young oospores is not obviously greater than that of the oospheres themselves. We regard the bodies in question as representing abnormal developments of oogonial cells, and not as being in any way concerned with fertilisation. Moreover, we have occasionally observed one cell in the divided oogonium, much larger than the rest, to contain two, or even sometimes three, nuclei, and these nuclei are then always close together. These facts have led us to reject Behrens’ account of the process.

A very large number of experiments were made, in order to determine, if possible, the time which elapsed between the addition of the antherozoids to the oospheres and the first division of the spore. A short summary of different sets of observations on is given in the subjoined tables.

S eries I.— Observations on Ascophyllum conducted at the Seaside, (a) The antherozoids were added to the oospheres at 10 o’clock a.m. Lot 1. Fixed 23 hours after the addition of antherozoids.

» 2, ,, 24 ,, i) ,, „ 3 & 4 „ 32 ,, ,, „ 5. „ 36 99 99 99 Nucleus preparing for division. Nucleus divided, rhizoid rudiment present* no dividing wall. Nucleus divided, no rhizoid, dividing wall present. Spore divided into about six cells. (6) The antherozoids added between 11 and 12 p.m. Lot 1. Fixed 24 hours after the addition of antherozoids. Nucleus divided, a few with rhizoid rudiments, and division wall. V, 2. „ 25 „ „ „ Same result. „ 3. „ 25 „ „ „ Not beyond spindle stage. „ 4. „ 28 „ Nucleus divided, no rhizoid or dividing wall*