37 



The most fiinclanieutal difference between sporophyte and gametophyte 

 lies in the fact tliat the latter possess just one-half as many chromosomes 

 as the former. This hereditary difference between sjjorophyte and gameto- 

 phyte and the change which brings about the transition may be made clear 

 by means of the following figure, showing diagramatically the behavior of 

 the chromatin. Fig. 1 illustrates the behavior of the chromatin in an ordi- 

 nary vegetative cell. Here the chromatin segments passing into the new 

 nuclei are formed by a longitudinal fission of a single chromosome — an 

 equational division. In Fig. 2, a to /, is shown the first or reducing divi- 

 sion in spore mother cells. One-half of the somatic chromosomes pass to 

 one of the daughter nuclei and the other half to the other, thus bringing 

 about the reduction of tlie number. The second division in the spore 

 mother cell (.'/ to /) is equational. 



Fig. 1. 



Fig:. 1. Diagrams showing the behavior of the chromatinlduring an ordinary somatic 

 mitosis, a. nucleus in resting condition, showing chromatin[distributed in small granules 

 within the linin network and a nucleolus, b. the chromatin spirem has formed and it has 

 split longitudinally, c. the spirem has segmented into chromosomes, e. g., eight, d. spin- 

 dle stage; chromosomes arranged in the equatorial plate, e. anaphase; daughter chromo 

 somes moving toward the poles of the spindle, f. daughter nuclei, each containing 

 eight daughter chromosomes. Such a division is known as equational, since the two re- 

 sulting nuclei are hereditarily alike. 



The parallel between plants and animals is found in the phenomenon 

 of the reduced number of chromosomes in the sex-cells, with this distinction, 

 that in higher plants the reduction in the number of the chromosomes oc- 



