18 LABORATORY AND FIELD EXERCISES 



B. ADJUSTMENT TO THE ENVIRONMENT 

 THE EMBRYO AND SEEDLING OF THE BEAN 



1. Structure of the seed and embryo. 



a. Eemove the protective seed coat from a soaked seed of 



a garden bean and study the embryo. The parts of 

 the bean embryo are similar to those of the pea 

 (Fig. 13 of the text). Compare with A and B, Fig. 7. 



b. Find the two large food-storing leaves, or cotyledons, 



comprising the bulk of the embryo. Remove one 

 cotyledon. Observe the plumule, or terminal bud of 

 the embryo, composed of two or three delicate leaves. 

 Find also the hypocotyl, or stem which bears both 

 cotyledons and plumule. The first, or primary, root 

 also grows from the end of the hypocotyl. 



c. Draw the parts of the embryo as they appear with one 



cotyledon removed. 



2. Adjustment of the embryo by tropisms or movements. 



a. Emergence of the embryo from the soil. How is this 



accomplished ? Sketch a plant which has just emerged 

 from the soil, indicating the position assumed by the 

 various organs. Contrast the bean with the pea and 

 morning-glory (Fig. 7). Label correctly. 



b. Adjustment of the organs of the bean to the environment. 



(1) Study two or three stages in the development of 



growing seedlings of beans. Observe the changes 

 in the position of hypocotyl, epicotyl, leaves, and 

 roots as development proceeds, 



(2) Sketch the most mature seedling observed, and also 



younger seedlings, to show the positions assumed 

 by the organs at each stage. Label all parts 

 correctly. 



