242 



MORPHOLOGY. 



while the other chromosome of each pair goes to the opposite 

 pole. The chromosomes here unite to form the daughter nuclei. 



Each of these nuclei now 

 divide as shown in figure 

 320 (whether the chromo- 

 somes in this second divi- 

 sion in the mother cell split 

 longitudinally or divide 

 transversely has not been 

 definitely settled), and four 



Different stages in the separation of divided nuclei are formed in the 

 U-shaped chromosomes at the nuclear plate. (After 



Mottier) In podophyllum. pollen mother cell. The 



protoplasm about each one of these four nuclei now surrounds 

 itself with a wall and the spores are formed. 



The number of chromosomes usually the same in a given 

 species throughout one phase of the plant. — In those plants 

 which have been carefully studied, the number of chromosomes 

 in the dividing nucleus has been found to be fairly constant in a 

 given species, through all the divisions in that stage or phase 

 of the plant, especially in the embryonic, or young growing 

 parts. For example, in the 

 prothallium, or gameto- 

 phyte, of certain ferns, as 

 osmunda, the number of 

 chromosomes in the divid- 

 ing nucleus is always twelve. 

 So in the development of 

 the pollen of lilium from 

 the mother cells, and in the 

 divisions of the antherid 

 cell to form the generative 

 cells or sperm cells, there 



Fig. 320. 

 Second division 



of 



Fig. 321. 

 Chromosomes uniting 

 are always twelve chromO- ""':1<=,' •", P°"™ mother at poles to form the 



.' c e 1 1 or podophylhim, nuclei 



somes so far as has been chromosomes at poles. 



;lei of the four spores. 

 (After Mottier.) 



found. In the development of the egg of lilium from the 

 macrospore there are also twelve chromosomes. 



