and Laboratory Methods. 1699 



condition to a colony, and from the condition of a colony to a multicellular plant. 

 By what means could this be accomplished ? The mechanical reason for the 

 division of one of these cells may be dependent on the following facts : All food 

 and waste material must pass through the wall. Now the surface of a sphere is 

 equal to ttD"^ and the volume is equal to ^ttD^, therefore, as the sphere 

 increases in size, the surface continues to become less in proportion to the volume. 

 How could a cell increase indefinitely in size and still keep the surface and 

 volume in about the same ratio ? What disadvantage or limit would there be to 

 such a process? These plants have potential immortality, i. e., they do not 

 grow old and die, except by accident. Natural death of an organism appears to 

 be an acquired character. This plant, with a number of others to follow, is 

 unicellular and without sexuality. It belongs to the lowest sub-kingdom of 

 plants, usually called the Protophyta. 



V. Meristnopedia sp. Class, Cyanophyceae. Order, Coccogonales. Family, 



Chroococcaceae. 



This organism can usually be found in the sediment of creeks, ponds, or 

 lakes, especially in shady places where there is some decaying vegetable matter. 



1. Mount some of the sediment and examine under high power. Look for 

 minute, blue-green, more or less rectangular plates of cells. Find colonies of 

 various sizes, select a perfect one and draw, showing the arrangement of the 

 cells. 



2. In how many directions does cell division take place ? How does the 

 colony break up into smaller pieces ? Such aflat layer of cells is called a super- 

 ficial aggregate. Neither plastids nor nuclei are visible in these cells. They 

 may be absent entirely. The bluish color is due to the presence of a peculiar 

 coloring matter in addition to the chlorophyll. Notice the gelatinous nature of 

 the cell wall. Write a careful description of the plant. 



VI. (a) Lyjigbya sp. Class, Cyanophyceae. Order, Psilonematales. 



Family, Oscillatoriaceae. 



The species known as Lyngbya wollei Farl, which produces large brownish- 

 black masses in rivers and ponds, or any other large species, may be used. A 

 large species, appearing like a brown or black slimy layer, quite common in 

 greenhouses and other moist situations, is also very good for study. This form 

 can be kept indefinitely in a moist jar of earth. 



1. Mount a small mass of the slimy material in water, and study under low 

 power. Draw several of the greenish-brown threads or filaments. Notice the 

 disc-like cells which make up the filament. Describe the general character of 

 these plants. 



2. Under high power study a single filament. Draw part of a filament, 

 showing the end cell. Why is the end cell more or less hemispherical and the 

 others disc-shaped ? Notice the dark granules. Where are they situated ? 

 Notice the thick sheath surrounding the cells. Draw a single cell. 



3. Study and describe the slow, oscillating movement of the filaments. Also 

 watch the movement of some short, free filaments. 



