266 THE TWO PHASES IN PLANT LIFE 



eral weeks, and more important still is the fact that this growth 

 occurs on the land where it is exposed to a wide range of stimuli 

 that cause it to vary in a most remarkable manner. So we must 

 bear in mind the character of this rather simple growth derived 

 from the gametospore of Ricciocarpiis 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 Spirogyra, 

 Vaucheria and Fuciis. 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 Ricciocarpiis the gametospore gives rise 

 to a varying number of cells that are difi^erent 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 131, one difiference 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 



