SEEDS AND SEEDLINGS 



69 



Make a series of at least three drawings of the developing seedling to show 

 the growth of the various organs In this series draw a line across your 

 paper to show the level of the ground. 



Problems cf Growth' — There are several interesting problems concerning 

 the growth of the bean seedling. Most of these questions we can solve 

 with the aid of simple experiments. 

 These experiments may bo allotted 

 to different meml)ers of the class 

 to perform at home and bring to 

 school when the laboratory work 

 of the bean seedling is finished and 

 the pupils are ready for a discus- 

 si L.n of its growth. The following 

 experiment should be started at 

 once. 



Experiment. — What is the func- 

 tion oj the cotyledons of the bean? 

 Plant six beans in sawdust. After 

 they have grown so that the hypo- 

 cotyls are above the surface, re- 

 move the cotyledons from three 

 beans. Watch the growth of both 

 lots very carefully, making sure 

 that they are exposed to exactly 

 the same conditions of heat, mois- 

 ture, light, and air. After two 

 weeks draw a bean from each lot. 

 Of what use to the growing plant 

 are the cotyledons? Why?^ 



'mm 



Bean seedlings. Note that in the older seed- 

 lings to the left the cotyledons have been 

 almost entirely used up. 



Germination. — All the stages 

 passed through by the youjig 

 plant, from the time the seed 

 begins to sprout until it can 

 take care oj itself by means of its roots and leaves, are known as the 

 stages of germinatioii. The young plant ceases to be a seedling after 

 it has lost its seed leaves or cotyledons. 



A comparison of the Pea and Bean. — Suggestions for laboratory work. 

 Compare the markings on the outside of the pea with those you found on 

 the bean. Make a diagram of the pea drawn from the hilum end. Show 

 the following structures neatly labeled : hilum, micropyle, strophiole. 



Open a soaked seed. How many cotyledons do you find? 



Plants having two cotyledons or seed leaves are called dicotyledons. Do 

 you know any other plants having two cotyledons besides the pea and bean ? 



* At this point, experiments may be introduced, showing the result of oxidation, 

 of organic materials, the tests for carbon dioxide, the fact that oxidation of food 

 substances takes place within the growing pea or bean (as shown bj^ placing ger- 

 minating seeds within a closed jar), and that air is necessary for germination. 



2 It must be remembered that this is not quite a fair test to the bean, because we 

 take away from the young plant part of its own body. 



