280 THE TWO PHASES IX PLANT LIFE 



wide range of stimuli that cause it to vary in a most remarkable 

 manner. So \ve must bear in mind the character of this rather 

 simple growth derived from the gametospore of Ricciocarpus and 

 compare it with the variations that appear in the succeeding 

 forms. 



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 gameto- 

 spore produced directly a plant like the parent, as in Vaucheria 

 and Fucus. In Spirogyra, Ulothrix, Oedogonium and Coleo- 

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

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

 produced cells or zoospores. The reason for this difference in 

 behavior is possibly due to the higher organization of the gameto- 

 spore. In the lower forms its first divisions result in the forma- 

 tion 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 consequence it forms a number of cells before cells like those of 

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

 certain 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 138, 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 

 contain, 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 re- 

 tained during the germination of the gametospore until the divi- 

 sion 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 



