EXERCISE XIII. 

 THE GROSS STRUCTURE OF SEEDS. 



Supplies for a Laboratory Section of Twelve. At least a dozen germinating lima beans from 8 to 10 days old J 

 germinating corn from 8 to 10 days old; dry and soaked lima beans; dry and soaked kernels of dent corn. 



Part A. Dicotyledonous Seed 



1. Remove the outer covering of a soaked lima bean, (a) Observe its elasticity and 

 strength, (b) Explain the use of such a covering. This covering may be called the seed-coat. 

 The scar found on the seed-coat is called the hilum . (c) Explain the presence of the hilum. 



2. Examine a bean which has grown to a height of three or four inches, (a) Compare the 

 two lower leaves with the two leaves just above, first as to shape, second as to thickness, 

 and third as to veins, (b) Compare the two halves of a soaked bean with the two lower 

 leaves of the young bean plant, (c) What relation do you observe to exist between the two 

 lower leaves of the young bean plant and the two halves of the seed? The halves of the 

 seed are called cotyledons. 



Fig. 8. A legume (Pea) pod showing manner in which 

 seeds are attached to pod. (Anderson) 



3. Between the cotyledons of the bean you will find the plumule. The word plumule 

 means a small feather, (a) What does the plumule appear to be? (b) What does this part 

 become in the young growing bean plant? 



4. The stem-like portion at one end of the cotyledons is called the hypocotyle — hypo, 

 below: cotyle, cotyledon. Examine sprouting lima beans found in the flower pots. Observe 

 what part the hypocotyle plays, in the growing plant. 



5. Make a careful drawing of one-half of a lima bean (about natural size) showing cotyle- 

 don, plumule, and hypocotyle in their proper positions. 



Part B. Monocotyledonous "Seeds." 



6. (a) On examining a kernel of corn what difference do you observe between the two 

 broader sides? (b) Remove the "germ" found just beneath the concave surface of one of 

 the two broader sides. It comprises about what fractional part of the whole kernel? The 

 portion of the kernel which is left is largely endosperm — food material stored for the use of the 

 young plantlet. 



7. With a sharp knife shave away the "germ" side of a kernel until two small cavities 

 appear. The cavity near the crown of the kernel contains a small body, the plumule. The 

 lower cavity, the one near the tip of the kernel, contains the primary root. The plumule, 

 the primary root, and the region lying between them may be called the embryonic plantlet 



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