80 TYPE STUDIES 



in the life history of the plant? How is it adapted for 

 its purposes ? Construct a series of diagrams that will 

 outline the life history of Spirogyra. What are believed 

 to be some of the advantages to an organism in having a 

 method of sexual reproduction? 



62. Cell structure of the moss leaf compared with Spirogyra. 



A. Mount a moss leaf in water and draw a group of cells under h.p., and 

 show details of protoplasmic structure in one of them. Note : 



1. That the chlorophyll is contained in numerous small, disk-shaped 

 bodies called chloroplasts. How are they distributed in the cell ? 



2. The multiplication of the chloroplasts by simple constriction. Draw 

 stages showing their division. 



B. Plasmolyze the cells with salt solution, and draw a group. Why do 

 adjacent cells have flat side walls '? 



C. Stain with iodine. 



1. Where are starch grains formed ? Draw. 



2. Where does the nucleus lie ? 



3. How much of the cell is filled with cell sap ? 

 93. The Amoeba (App. 7). 



A. Gather with a pipette some of the slime at the bottom or scum on 

 the top of a culture of AmoebcB. Search, under m.p., for transparent, 

 naked cells which slowly change their outline, by thrusting out some 

 processes, pseudopodia, and withdrawing others. 



B. Stvidy under h.p. the changes in form of an Amoeba as it slowly moves 

 along, making a series of outline sketches. Note the flow of the gran- 

 ular cytoplasm into the pseudopodia as they are formed. 



C. Draw diagrammatically an individual on a large scale, showing: 



1. The plasma membrane, colorless and without granules. 



2. The granular cytoplasm inclosed by the plasma membrane, fre- 

 quently containing food inclusions, as, for example, one-celled plants 

 such as diatoms and desmids. How would you expect this food to 

 be taken into the interior of the Amoeba ? 



8. A dense spherical nucleus (not always easily found). 



4. Vacuoles which form, and later suddenly disappear, and consequently 

 are called contractile vacuoles. 



D. The Amoeba, as is generally the case with an animal cell, is a naked 

 protoplast. Compare with a typical plant cell. What does one have 

 that is lacking in the other t^ What do both have in common ? 



The Amoeba reproduces by construction, a single individual thus forming 

 two similar daughter Armjcboi (see Principles. Fig. 107. B). 



