EXERCISE 30 



There are many kinds of plant structures besides seeds that are used for producing new individual 

 plants, and that are really different. Pieces of potato containing eyes are sometimes called seeds, and 

 so are grains, like wheat, barley, corn, etc. 



Problem. How does a grain differ from a seed ? 



What to use. Corn grains, some dry and some cooked on the cob (and preserved in dilute 

 formalin solution) ; magnifying glass ; iodine solution. 



What to do. Examine the grains, dry and cooked, and locate (i) the point of attachment to the 

 cob ; (2) the little spot at the opposite end at which the silk was attached ; (3) the flat, shield-shaped 

 area marking the position of the embryo. 



Carefully remove the coat of a cooked grain without injuring any of the structure beneath. Note 

 two rodlike structures appearing just below the surface of the embryo. The one pointing toward the 

 cob is the hypocotyl ; the one pointing toward the silk is the plumule, or epicotyl. The rest of the 

 embryo is cotyledon. 



Carefully break out the embryo from the rest of the grain. Note how the cotyledon part differs 

 from the corresponding part in the seeds studied. 



NOTE I. The part of the grain left after removal of the embryo is called endosperm; it is a mass of food which is 

 used by the embryo after it sprouts. Many kinds of seeds also have endosperm. 



Cut a cooked grain through from the embryo side, passing through the plumule in some and through 

 the hypocotyl in others ; cut some through lengthwise, splitting down the face of the embryo. Place 

 the cut grains in iodine solution for a few minutes. This will stain the grain so that the embryo is 

 distinct from the endosperm. 



Examine the cut surface of several grains, to make up your mind what the shape of the embryo is. 



Record. Make diagrams called for in the table on the next page at least three times as large as the 

 original object. Label in each drawing all the structures that have been mentioned in the study. 



Questions. 1. What structures are present in both the seed and the grain ? 



2. What structures has the grain that are not present in the seed ? 



3. What structure has a seed that a grain has not ? 



4. What serves the bean or pea embryo in the way the endosperm serves the corn embryo ? 



NOTE 2. Plants whose embryos have two cotyledons are called dicotyls or dicotyledonous plants ; those whose embryos 

 have but a single cotyledon are called monocotyls or monocotyledonous plants. 



5. Name six dicotyls. 



6. Name six monocotyls. 



7. What is your definition of a grain ? 



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