Elementary botany . etransversely has not beendefinitely settled), and four Different stages in the separation of divided nuclei are formed in theU-shaped chromosomes at the nuclear plate. (After Mottier) in podophyllum. pollen mother cell. The protoplasm about each one of these four nuclei now surroundsitself with a wall and the spores are formed. The number of chromosomes usually the same in a givenspecies throughout one phase of the plant.—In those plantswhich have been carefully studied, the number of chromosomesin the dividing nucleus has been found to be fairly constant in agiven species
Elementary botany . etransversely has not beendefinitely settled), and four Different stages in the separation of divided nuclei are formed in theU-shaped chromosomes at the nuclear plate. (After Mottier) in podophyllum. pollen mother cell. The protoplasm about each one of these four nuclei now surroundsitself with a wall and the spores are formed. The number of chromosomes usually the same in a givenspecies throughout one phase of the plant.—In those plantswhich have been carefully studied, the number of chromosomesin the dividing nucleus has been found to be fairly constant in agiven species, through all the divisions in that stage or phaseof the plant, especially in the embryonic, or young growingparts. For example, in theprothallium, or gameto-phyte, of certain ferns, asosmunda, the number ofchromosomes in the divid-ing nucleus is always in the development ofthe pollen of lilium fromthe mother cells, and in thedivisions of the antheridcell to form the generativecells or sperm cells, there. Fig. division of Fig. 41Chromosomes uniting are alwaVS twelve chroniO- nucle| in pollen mother at poles to form the^ ^ c e 1 1 of podophyllum, nuclei of the four spores. SOmeS SO far as has been chromosomes at poles. (After Mottier.) found. In the development of the egg of lilium from themacrospore there are also twelve chromosomes. 344 MORPHOLOG Y. When fertilization takes place the number of chromosomesis doubled in the embryo.—In the spermatozoid of osmundathen, as well as in the egg, since these are developed on the game-tophyte, there are twelve chromosomes each. The same is truein the sperm-cell (generative cell) of lilium, and also in the egg-cell. When these nuclei unite, as they do in fertilization, thepaternal nucleus with the maternal nucleus, the number of chro-mosomes in the fertilized egg, if we take lilium as an example,is twenty-four instead of twelve; the number is doubled. Thefertilized egg is the beginning of the sporophyte, as we ha
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