GENERAL BIOLOGY 



lished turn cork sheet through 90 or 180 and observe subsequent 

 directions of growth of roots and stems. 

 Sketch experiment and explain results. 



2. Demonstration of Phototropism. 



a. Stem and leaves. Place growing seedlings of beans, corn or 

 oats in a dark box open on one side toward the light and observe 

 the leaf and stem positions after a few days. 



b. Roots. Place seedlings of radish grown in a jar of water in 

 a dark box illuminated from one side and observe direction of 

 growth of roots. 



What is the influence of light on the direction of growth in 

 shoots and roots? 



3. Hydrotropism. 



Plant various seeds in an inclined trough of wire netting filled 

 with wet sawdust. Observe and explain the direction of growth 

 of the roots. 



SPIROGYRA. 



Read: Huxley and Martin, Practical Biology, pp. 397-407; or 

 Parker, Elementary Biology, pp. 192-198; or 

 Woodruff, Foundations of Biology, p. 61. 



(Subkingdom Cryptogamia, Division Thiallophyta, Subdivision 

 Algae, Class Chlorophyceae.) 



1. Place a few filaments of the living plant in water on a 

 slide, cover and examine with low power. Draw a small portion of 

 one of the filaments showing its division into cells. 



2. Examine with high power. Note the cell walls and the 

 connection between adjacent cells. Note also in each cell the long, 

 band-like, green chloroplastids. Count them and make out their 

 arrangement. Make a drawing about two inches in length of a 

 single cell, showing the chloroplastids and the connection with 

 adjacent cells. 



3. Treat the preparation with iodine solution. Note the changes 

 of color in the rounded bodies imbedded in the chloroplastids. 

 These are reserve food bodies (pyrenoids), and their blue color 

 after treatment with iodine indicates the presence of starch. 



4. Examine the cell wall carefully and note the thin layer 

 of cytoplasm which lines it internally, and the large vacuole filled 

 with cell sap, which occupies the greater part of the cell. Focus 



[28] 



