154 APPLIED BIOLOGY 



tion, especially in seeds like bean with so much stored food 

 that the cotyledons cannot do well the work of leaves and 

 in seeds like corn and pea with cotyledons that do no work 

 as leaves. Under such conditions it is important that the 

 seed have a well-developed epicotyl ready to put forth leaves 

 at an early stage of germination. In seeds like the squash 

 with cotyledons which are leaf -like, the leaves from the 

 epicotyl are not needed so early and there is time for 

 further development of the small epicotyl after germination 

 begins. 



When you notice either a large or small epicotyl in a seed, look 

 for such relations of the work of the cotyledons as is suggested in 

 paragraph above. 



In cases like corn and pea where the hypocotyl does not push up 

 the cotyledons, the epicotyl lengthens and rises above the ground. 



144. The Hypocotyl. It has been noted in the laboratory 

 work that in the seeds of squash and bean the hypocotyl 

 of the ungerminated seed develops into part stem and part 

 root. In these cases the stem part of the hypocotyl grows 

 in length and pushes the cotyledons upward out of the soil, 

 while the root is growing down into the soil. The stem part 

 of the hypocotyl of the pea and corn does not lengthen, and 

 so the cotyledons remain below ground, their place as first 

 leaves above ground being taken by the epicotyl. 



145. Conditions of Germination. It is easy to demon- 

 strate that water, oxygen (from air), and proper temperature 

 are necessary for germination. 



Water. That water is necessary requires no special 

 experimental proof, for every one knows that seeds kept dry 

 remain dormant, and that seedlings do not " come up " 

 in gardens when the soil is dry, as in midsummer. Many 

 hard-coated seeds have special ways of letting in the necessary 

 water, such as the spongy mass at end of castor-bean, and 

 the holes in a cocoanut. Other seeds must remain in the soil 



