Sexual Reproduction and the Organization of the Nucleus in Certain Mildews Volume 37 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1905 edition. Excerpt: ...Maire has evidently seen more than four chromosomes in many cases in the prophases, but maintains his contention by calling these more numerous bodies " prochromosomes " and asserting that they later fuse into four true chromosomes. He will hardly maintain, however, that the bodies shown on the spindle in fig. 55 are prochromosomes, and there can be no question that there are at least eight of them on each half of the spindle. With poor fixation it is possible to find the chromosomes of the mildew fused together into irregular masses, as may happen also in the pollen mother cells of the larch or lily, and it is doubtless such cases of poor fixation which have misled Maire and Dangeard. The polar asters at these stages are very strongly developed, and it is apparent that some of the astral rays extend to the plasma membrane of the ascus. The central spindle fibers left after the chromosomes have reached the poles seem to disintegrate and pass over into the general cytoplasmic substance (figs. 56, 57). Frequently they may be much elongated by further separation of the young daughter nuclei, but this is not necessary to their disappearance. The chromosomes are next found loosely aggregated at the poles and still plainly connected to the central body by the fibers which drew them back from the equatorial plate region (fig. 56). This results in a sort of diaster stage (fig. 57), though the significance of the name does not appear in any conspicuous arrangement of the chromosomes. A nuclear membrane is next formed, close in to the surface of the chromosomes at first, but soon expanding so that more or less clear space appears around the mass. The chromosomes themselves seem to be the cause of this enlargement. They grow in length backward from the...