CYTOLOGY OF PLANTS 307 
stamens or with pistils, or more usually with both, we 
find that the x-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 2x-generation 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 x-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 x-generation thus represented is never set free, 
but remains enclosed in the tissues of the 2x-generation 
right up to the time of fertilization. In the process 
of fertilization the double number of chromosomes 
characteristic of the 2x-generation is once more 
arrived at. 
We can look upon the 2x-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 
20—2 
