and Laboratory Methods. 1935 



pens ? How long are the flagella, compared with the size of the body ? Look 

 for the nucleus. Notice the protoplasmic strands which pass from the cell-body 

 to the wall. 



6. Notice the division of labor in the organism and designate the function 

 of the following organs : a, cell wall ; b, flagella ; c, chloroplasts. 



7. Make a diagram in the notes showing the life cycle of Sphaerella when 

 reproduction takes place by the formation of non-sexual zoospores. (See 

 Fig. 4 a.) 



8. Look for individuals divided into six or eight cells. Draw. When these 

 escape they are smaller than the four and at first have no cell walls. These 

 zoospores are said to conjugate and form zoozygospores as is the case in Sphce- 

 rella bvetschlii. Careful observations should be made in order to discover such a 

 process. In case conjugation takes place the life cycle during this stage maybe 

 represented as in Fig. 4 b. 



XV. Pandorina morum (Muell.), Bory. 



Order, Protococcales. Family, Volvocaceae. 



Pandorina occurs in small pools of water, and is often very abundant in 

 summer, coloring such pools a bright green. The individuals consist of a free- 

 swimming colony of sixteen cells, and are more or less globular or oval in outline. 



1. Mount some of the colonies in water and examine under low power. 

 Notice the active movement. Draw a colony under high power. If they can- 

 not be followed because of their active movements, add a drop of carbolic acid 

 water. 



2. Notice the details of an individual cell of the colony ; the two flagella, the 

 red eyespot, the transparent spot in the outer end of the cell, and the chloroplast 

 with a pyrenoid. 



3. Study and draw colonies in stages of division. Each of the sixteen cells 

 divides until each forms a group of sixteen new cells, then the gelatinous envelope 

 dissolves and the sixteen daughter colonies are set free. This is the normal 

 method of vegetative propagation. 



4. Sexual reproduction. Look for colonies in which the cells are separating 

 as isolated zoospores. These are the gametes which are very much alike, but 

 are of various sizes. 



5. Watch for conjugating forms. Conjugation takes place between two 

 gametes of equal size, or between a larger and a smaller one. The process is 

 complete in a few minutes. Draw stages observed, and also mature zygospores. 

 The difference in size of the conjugating gametes is of special importance, since 

 it is the first step in the evolution of two specialized gametes, the oosphere and 

 spermatozoid. 



6. Note. — Pandorina is well preserved in water with carbolic acid, and large 

 quantities may be collected at the proper season, showing the various stages of 

 the life cycle. Cultures can also be obtained in the laboratory from dry zygo- 

 spores. John H. Schaffner. 

 Ohio State University. 



