The Algae 447 



smaller in size. In the more specialized forms the male gamete 

 is a small, free-swimming cell (sperm), and the female gamete 

 (egg) is a large, non-motile cell containing a large amount of food 

 materials. The cell in which the sperms are formed is called an 

 antheridium (plural, antheridia), while the cell that forms an egg 

 is called an oogonium (plural, oogonia). The spore formed by 

 the union of a sperm and an egg is called an oospore. 



In the peculiar group to which Spirogyra and Zygnema belong, 

 the gametes unite through a tube that forms between the two 

 gamete-producing cells. There are neither swimming spores 

 nor free-swimming gametes. 



Distribution. Green algae are comparatively abundant in 

 tropical seas and decrease rapidly in number along the northern 

 coasts. On land they are most numerous in fresh-water ponds, 

 pools, and streams of the temperate zone. The small forms occur 

 in every conceivable habitat. Some of them cause the red 

 patches on snow banks in the arctic regions and on high moun- 

 tain tops. 



Protococcus. On the partly shaded, moist sides of trees, rocks, 

 buildings, and fences everywhere, there occur patches that look 

 as if they had been stained green. If a little of this stain is 

 scraped off and examined under a microscope, it is seen to be 

 made up of little, rounded green cells. Each cell consists of a 

 cell wall, cytoplasm, and nucleus. In the cytoplasm is a large 

 green plastid which almost fills the cell. 



When the cells are examined, certain of them will be found to 

 be elongated ; some of these may be dividing into two. Some- 

 times there are two or more cells still clinging together, showing 

 clearly that they have just been formed by division. These 

 groups separate readily when the cover glass is tapped, and each 

 single cell may go on living quite independently of the others. 

 The plant, therefore, consists of a single cell which carries on 

 all the essential processes of life and is able to reproduce itself. 

 Moreover, it is a highly successful plant, for Protococcus occurs 



