70 



BOTANY 



Most of our trees, and vevy many of our common plants, belong to this 

 great group of plants. 



How many of the parts inside the cotyledons can you identify and com- 

 pare with similar structures in the bean? Look for hypocotyl, epicotyl, 



and true leaves. Are the structures 

 named homologous with the same 

 structures in the bean? How do 

 3'ou know? 



Draw the pea, showing all the 

 above-named parts. 



Compare the pea seedling and 

 bean seedling with regard to the 

 following points: (1) as to the 

 method of getting out of the ground; 

 (2) as to the part which appears 

 first; (3) as to the parts that ap- 

 pear above ground ; (4) the ultimate 

 fate of each part. 



This must be made the subject 

 of an extended home experiment. 

 Drawings should be made to illus- 

 trate each stage of growth, and each 

 part should be carefully labeled.^ 



An experiment to prove the func- 

 tion of the cotyledons of the pea 

 may be made in very much the 

 same way as the experiment per- 

 formed to find out the same thing 

 for the bean. This experiment can 

 be made at home and brought in 

 at the same time as the bean ex- 

 periment, and comparisons made. 



Experiment to show the function of the coty- 

 ledons of the pea, photographed at the 

 end of two weeks. Note the size of the 

 plants at the left, without cotyledons. 



Analogy. — A structure which has the same function or use as 

 another structure is said to be analogous to it. Is the cotyledon of 

 the pea analogous to the cotyledon of the bean ? Is it also ho- 

 mologous? 



Cotyledons as Foliage Leaves. — In the young plants which we 

 have just been talking about, the cotyledons hold a reserve food 

 supply, but do not serve at any time as true leaves for the plant 

 In many dicotyledons, however, the seed leaves do act as true 

 leaves. This may well be seen in the squash seedling. Here the 

 young plant has little or no food stored in the cotyledons; it 

 must be prepared to take care of itself quickly. It does this by 

 means of the rapidly growing cotyledons, which soon unfold as 

 true leaves to the sun. In the seeds of the pea and bean we have 

 found that the embryo takes up all the space within the seed 



^ See Hunter and Valentine, Manual, page 18. 



