2 REPRESENTATIVE PLANTS 



Seed coat. With a pin, needle, knife, or even with the 

 finger nail, very carefully cut or tear the skin {seed coat or 

 testa) the whole length of the convex margin ; remove and 

 study. Observe its firmness. Examine the skin, and the 

 part removed from it, and find which one bears the three 

 marks named under "External Features." Pass a pin into 

 the pore and discover in what structure it appears, on tlie 

 inside. Look at the seed proper and find a structure that 

 " fits " into this depression. Keep this point in mind when 

 you study sprouting seeds. 



The seed proper. Examine the seed you have removed from 

 the seed coat. Carefully separate the large halves (cotyle- 

 dons or seed leaves) until they break apart. The little 

 structure lying between the cotyledons and fastened to each 

 is the little plant. This with a lens may easily be seen to 

 consist of a little stem (hyjyocotyl) and a pair of tiny leaves 

 (plumule). Observe that the cotyledons are attached to the 

 larger upper end of the hypocotyl (points where leaves are 

 attached to a stem are nodes) ; with the lens find a small, 

 short, stemlike part connecting this point with the plumule 

 (the embryo stem). The cotyledons and the little plant 

 connecting them (all there is in a bean seed) is the embryo. 



Drawings. 1. Draw a seed, side, hilum, margin, and end 

 views. 2. Draw the seed with the cotyledons separated 

 and their concave margins next to each other, with the little 

 plant in place. 3. Draw the little plant (x4). 4. Draw 

 three cross sections at different points. 



Other work. Experiments. Seeds that may be easily sep- 

 arated (on soaking) into similar halves are Dicotyledons, 

 (two cotyledons). What is the purpose of the large cotyle- 

 dons ? What other seeds do you know that have the two 

 cotyledons ? Try this experiment : Scrape some of the 

 soaked bean and apply weak iodine solution to the scrap- 

 ings and observe the change of color. This shows what sub- 

 stance in the bean? (Test in the same way some corn- 



