EXERCISE 60 

 THE COTYLEDONS 



Materials. Young plants and seeds as used in the preceding 

 exercise, in various stages of growth; iodine solution. 



Directions for work. It will be found that it is frequently 

 stated that the cotyledons are in fact leaves. What facts can 

 you discover that appear to confirm or to dispute this state- 

 ment? Study several kinds of seedlings. Do the cotyledons 

 have either of the types of arrangement that you have found 

 to be characteristic of the arrangements of leaves on a stem ? 

 Are there buds in the positions where you should expect to 

 find buds if the cotyledons are in reality leaves ? Do the coty- 

 ledons of any plants studied perform the work of leaves ? 



What special work do cotyledons, or at least some of them, 

 perform that is different from the usual work of leaves? Ex- 

 amine a series of cotyledons from a bean or a peanut plant. 

 Note any changes in the plumpness and apparent volume of the 

 cotyledons as they grow older. Break open the cotyledons and 

 test the interiors for starch. What differences in this particular 

 do you find between older and younger cotyledons? If you 

 can find some plants that are old enough so that the cotyledons 

 are about to fall off, include them in the test, or let some of 

 the plants grow and watch the fate of the cotyledons. What 

 does your study indicate as to the office which the cotyledons 

 are performing? 



References 



BERGEN and CALDWELL. Practical Botany, pp. 142-144. 

 BERGEN and CALDWELL. Introduction to Botany, pp. 158-165. 



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