GREEN ALGM 2IQ 



This formula may be abbreviated by the use of signs as follows : 

 P P P ( g > E - P, etc., in which P stands for plant 



and its repetition indicates multiplication of the plant from simi- 

 lar parts, not by means of special reproductive or propagative 

 bodies; g = gamete, E = the fertilized egg, zygospore or oospore, 

 as it is called in special cases. 



Sporophyte 



- ^termination. 

 Egg^NT- 



Diagram No. I. Illustrating the life cycle in the development of Spirogyra. Course 

 of development follows the direction indicated by arrows. Zygote equals fertilized egg, 

 which in this case is the zygospore. 



358. Zygnema. Zygnema is another genus of filamentous 

 algae closely related to Spirogyra. It differs chiefly in the form 

 of the chlorophyll bodies. These are star-shaped and two in 

 a single cell. The nucleus in the cell is not so conspicuous. 

 Growth, multiplication and conjugation take place as in Spiro- 

 gyra. The life history follows the same course and the plant is 

 found under similar conditions. 



359. The desmids. The desmids form another family of 

 conjugating algae. They are mostly single-celled plants of very 

 beautiful form and markings, while a few of them unite into 

 filaments. They occur in fresh water, often mingled with spiro- 

 gyra and other green algae. The single-celled forms are bisym- 

 metrical, each half being exactly like the other. They multiply 

 by dividing so as to separate these two halves, and each half then 

 reproduces a new one in place of the lost half. They conjugate 

 by the protoplasts (the cell content) from two cells separating 

 from the cell wall and uniting to form a zygospore which is thick- 

 walled and often beautifully sculptured. 



