THE ORIGIN OF SEX IN PLANTS 



ii 



structurally resembles many simple Plants. Whether 

 in the motile or the encysted phase it shows its primitive 

 character by being unicellular, and by the absence of 

 any sexual mode of increase. 



Another simple example is seen in Protococcus viridis, 

 which is commonly found growing as a fine green powder 

 on the windward side of tree-trunks in damp climates. 

 The single cell is stationary, 

 spherical, and bounded in a 

 cell- wall (Fig. 5). In these 

 respects it resembles the 

 encysted Euglena. Each 

 cell may divide, and the 

 divisions may be repeated, 

 so that a group of cells is 

 formed. But sooner or 

 later they round off and 

 separate, each being in fact 

 an independent individual. 

 Here again no sexual pro- 

 cess is known. In being 

 non-motile, encysted, and 

 containing green chloro- 

 phyll, Prolococcus shows features that are usual in Plants. 

 It is accordingly referred to the Plant-Kingdom. These 

 two examples will serve to suggest that very minute and 

 simple creatures exist, some of which are difficult to refer 

 to the one Kingdom or to the other ; and that they show 

 no sexual process whatever. They are probably very 

 primitive living beings, such as in Evolution preceded the 

 introduction of Sex. 



The next example is Ulothrix, a small green Alga found 

 very commonly attached to stones in fresh-water streams. 



FIG. 5- 



Protococcus viridis, a unicellular plant, existing 

 singly, or in groups. ( x 730.) 



