USEFUL ALGAE — CHASE 407 



Many species of seaweeds, fresh from the sea, can resist the action 

 of fresh water while others instantly dissolve and decompose in fre&.h 

 water. 



In the lowest forms of algae where the whole body consists of a 

 single cell, some cells gradually change and are converted into a 

 spore or fruiting body without any obvious contact with other cells. 

 More frequently, as in the Desmidiaceae and Diatomaceae, a spore 

 is formed only by the conjugation of two cells or individual plants. 

 When the two cells are mature, usually filled with darker-colored 

 chlorophyll, they approach each other. A portion of the cell wall 

 of each one is then extended into a tubercle at opposite points. The 

 tubercles come in contact and become confluent as the cell wall be- 

 tween them vanishes and a tube thus connects the two cells. The 

 contents of the cells are mixed through this tube and a sporangium, 

 or new cell filled with spores, is formed either in one of the old cells 

 or at the point of the connecting tube. Then the old, empty cells 

 die while the sporangium may remain dormant for a year or several 

 years. These sporangia which are formed in abundance at the close 

 of the growing season become buried in the mud at the bottom of 

 pools where they are encased when the water dries up in the summer, 

 then in the spring with the return of water they develop new fronds. 



The filamentous algae of the pools and ditches also form new plants 

 in this manner. Almost every cell of these filaments is fertile and 

 when two filaments are joined together a series of sporangia will be 

 formed on one filament while the other is converted into a string of 

 dead, empty cells. 



In the highest algae there appear to be two sexes. The sporangium 

 is fertilized when it is in its most elementary form and when it 

 cannot be distinguished from an ordinary cell. The fertilizing 

 organs are called antheridia and are most readily seen among the 

 Fucaceae. 



Besides reproducing by single spores many algae have another and 

 sometimes a third means of reproduction. 



As has already been mentioned, the simplest algae divide by the 

 division of a single cell into two cells. 



In the green algae, the homogenous, semifluid consistence of the 

 cell becomes granulated. The granules detach themselves from the 

 cell wall and float freely in the cell. At first they are irregular in 

 shape but gradually they become spherical. They congregate in a 

 dense mass in the center of the cell and a movement similar to 

 that of bees around their queen commences. One by one the active 

 zoospores detach themselves from each other and move rapidly 

 about in the vacant space in the swarm cell. They continually push 

 against the cell wall until it is broken, when their spontaneous move- 



