Nucleolus in Root Tip Mitosis in Zea mays

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Abstract
By the use of different fixatives it was possible to fix: (1) chromatin, plastin, and mitochondria; (2) chromatin, plastin, and dissolve all mitochondria; (3) plastin and mitochondria, and dissolve the chromatin; (4) chromatin, and dissolve or render unstainable all plastin and mitochondria; and (5) plastin, and dissolve all chromatin and mitochondria. It was thus possible to investigate the behavior of the nucleolar material during cell division unobscured by any chromatin or mitochondria. In the resting nucleus all chromatin is localized in the reticulum, the nucleolus containing none. After the spireme is formed the nucleolus becomes connected with it, and later becomes pear-shaped, the point of attachment being at the small lobe of the pear. As the spireme flattens out on the equatorial plane nucleolar material flows into it. The smaller lobe of the nucleolus is drawn out and splits in 2, giving the nucleolus 2 connections with the spireme. As the nucleolus loses material it becomes rod-shaped, and finally lies at right angles to the plane of division. It is drawn out, constricted in 2, and the 2 fragments round up and migrate to the poles. There they break up into small granules, some of which, possibly all, pass into the cytoplasm where they later disappear. In telophase the nucleolar material which had been incorporated in the chromosomes collects into small globules which later fuse to form the daughter nucleolus. Nucleolar material is thus continuous, and is derived from previously existing nucleolar material. Some, however, is apparently lost during each cell division. Two possible explanations of the function of the nucleolar material are added to those already proposed. (1) The plastin, by entering into the chromosomes, coming into intimate contact with the genes during cell division, and passing in part out into the cytoplasm during the subsequent division, may serve as a vehicle for transmitting the influence of the genes to the organism. (2) The plastin, being electro-positive, changes the electro-negative spireme by flowing into it, to an electro-positive chromatin complex; thus the chromatin, which had collected at the equatorial plate as far as possible from the poles of the spindle, reverses its motion with its electrical charge and migrates to the 2 poles.

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