DEVELOPMENT OF PLANTS 2531 



It is also evident that the fusion of the gametes in the simple 

 liverworts results in the production of a cell, the gametospore, 

 that is radically different in its nature and possibilities of growth 

 from any of the cells of the parent plant or liverwort. This was 

 not apparent in the simpler forms of the algae, where the gamet- 

 ospore produced directly a plant like the parent, as in Spirogyra, 

 Vaucheria and Fucus. In Ulothrix, Oedogonium and Coleo- 

 chaete, we saw the first indication of the real nature of the game- 

 tospore. It did not develop into a plant like the parent, but pro- 

 duced zoospores. The reason for this difference in behavior is 

 possibly due to the higher organization of the gametospore. In 

 the lower forms its first divisions result in the formation of cells 

 that are of the same nature as the cells of the parent plant, but 

 in higher forms its composition is more complex and as a conse- 

 quence it forms a number of cells before cells like those of the 

 parent plant are developed. For example, in the Red Algae, cer- 

 tain of the fungi and in Ricciocarpus the gametospore gives rise 

 to a varying number of cells that are different from those of the 

 parent plant, but finally spore mother cells are formed from which 

 are derived spores that are of the same nature as those of the 

 parent plant and that consequently produce new plants like the 

 parent. As has been stated on page 124, one difference between 

 the cells derived from the gametospore and those of the parent 

 plant is to be found in the number of chromosomes which they con- 

 tain, the former having twice as many chromosomes as the latter. 

 The doubling of the chromosomes occurs when the two gametes 

 unite to form the gametospore and this number is retained during 

 the germination of the gametospore until the division of the spore 

 mother cells, which results in the formation of spores with only 

 one half the number of chromosomes. In the lower algae this 

 reduction must occur in the first divisions of the germinating 

 gametospore, which therefore corresponds to the spore mother 

 cell, but in the Red Algae and Ricciocarpus a considerable growth 

 intervenes before the spore mother cells appear and the reduction 

 of the chromosomes takes place. In other words, as we ascend 

 the scale of plant life, the formation of the spore mother cells and 

 the reduction of the chromosomes is preceded by an ever-increas- 



