56 PHYSIOLOGICAL PROCESSES IN PLANTS 



a. Relation of Embryo to Food Supply 

 1. INTERNAL STRUCTURE 



Observations. 1. Remove the outer coat (testa) of a 

 soaked bean. Look for another coat under it. 



2. Into how many parts (cotyledons) does the rest of the 

 bean naturally separate ? 



3. Remove one cotyledon (seed leaf) very carefully, and find 

 some minute leaves (plumule). Where are they situated? 



4. Find a rodlike part (hypocotyl). 



Note. The plumule later develops into the first true leaves 

 of the plant, while the hypocotyl develops into the root and 

 lower stem. The embryo includes all the parts of the seed 

 that will later develop into parts of the young plant. Name 

 these parts. 



Conclusions. 1. What do you think is the use of the seed 

 coats ? 



2. What structures suggest the stem of the developed plant ? 

 Root ? Leaves ? 



3. How has the embryo been fed and protected up to this 



2. FOOD SUPPLY OF THE EMBRYO 



Note. For food tests see Prob. Ill, or, see Hunter, Essen- 

 tials of Biology, Chap. V. 



Observations. 1. Crush a bit of soaked bean cotyledon, 

 and add a few drops of iodine solution. What results ? 



2. Put some of this material on a glass slide and view 

 through the demonstration microscope. Find small oval bodies 

 stained bluish or black with the iodine. 



Conclusions. 1. What food material is in the cotyledon ? 

 Proof ? 



2. What are the oval bodies seen through the microscope ? 



Observations. 1. Add nitric acid to some crushed cotyledon. 

 What color appears ? Rinse off the acid, and add ammonia. 

 What color ? 



