CYTOLOGY OF PLANTS 



273 



stamens or with pistils, or more usually with both, we 

 find that the ^-generation has become still further 

 reduced, so that it no longer occupies an independent 

 phase of the life -history, but has come to be entirely 

 dependent upon the 2#-gene ration for its support. 



A plant which bears both stamens and pistils gives 

 rise to spores of two kinds, differing greatly in size. 

 The smaller spores are represented by the pollen-grains, 

 and in these, after one or two cell divisions, unaccom- 

 panied by growth, the one or two male gametes are 

 produced. The small association of cells arising in this 

 way is all that is left of the ^-generation on the male 

 side. 



The nucleus of the larger spore also divides a few 

 times, and one of the final products of division becomes 

 the ovum. Spore and ovum, as well as the few inter- 

 vening cells, bear the reduced number of chromosomes. 

 The ^-generation thus represented is never set free, 

 but remains enclosed in the tissues of the 2#-generation 

 right up to the time of fertilization. In the process 

 of fertilization the double number of chromosomes 

 characteristic of the 2#-generation is once more 

 arrived at. 



We can look upon the 2#-generation of the higher 

 plants as being formed by an expansion of the fertilized 

 ovum. The zygote, instead of comprising a single cell 

 only, by dint of delaying the reducing division, has 

 come to consist of a great mass of cells, all the nuclei 

 of which contain the double number of chromosomes. 

 This fact is also our excuse for applying the same term 

 of zygote to the cell produced by the conjugation of 



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