SEEDS AND SEEDLINGS 



79 



germination. All the stages 

 passed through by the young 

 plant, from the time the seed be- 

 gins to sprout until it can take 

 care of itself by means of its 

 roots and leaves, are known as 

 the stages of germination. 



In the pea, growth is like- 

 wise at first made largely at 

 the expense of the cotyledons, 

 which never rise above ground. 

 Removal of the cotyledons from 

 half the number of one lot of 

 germinating peas, and exposure 

 to the same conditions as the 

 other half of the same lot, shows 

 that the loss of the cotyledons 

 retards growth and may result 

 in the death of the seedlings. 1 



Experiment to show the function of the 

 cotyledons of the pea, photographed at 

 the end of two weeks. Note the size of 

 the plants at the left, without cotyle- 

 dons. 



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

 just been studying, the cotyledons hold a reserve food supply, but 

 do not serve at any time as true leaves for the plant. In many dicoty- 

 ledons, however, the seed 

 leaves do act as true 

 leaves. This may well be 

 seen in the squash seed- 

 ling. 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 coty- 

 ledons, 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 coats. There are some dicotyledonous 

 plants that have food stored outside of the embryo. Such a plant is the 

 castor bean. A section cut vertically through the castor bean discloses 



- d 



Arrangement of embryo in endosperm (GRAY) : 

 a, morning-glory ; b, barberry ; c, potato ; d, four- 

 o'clock. 



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

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



