Seeds and Seedlings. ai 



not germinate, although all other conditions are favorable. 

 The oxygen serves a double purpose in helping to form 

 new soluble and diffusible compounds from the reserve 

 materials, and in sustaining the respiration of the embryo 

 as it becomes quickened into renewed growth. The neces- 

 sity of oxygen to germination has been demonstrated by 

 Experiment 40, page 15, but it is also frequently demon- 

 strated in nature by the fact that most seeds will not 

 germinate in a water-soaked soil; 



notable exceptions are the seeds ^ 



of some water plants, such as 

 those of Nelumbo, which are able 

 to obtain sufficient oxygen from 

 the water. • 



11. Digestive Ferments. — The 



Fig. 3. 



insoluble and poorly diffusible 



■' Photomicrograph of starch Grains 



reserve materials are rendered from a grain of Indian com in 



soluble and diffusible by means ^" advanced stage of germina- 



•' tion. 



of ferments present in the seeds. 



The ferment which attacks starch is known as diastase. 

 The result of its work can be seen by a comparison of 

 Figs. 2 and 3, which are photomicrographs of starch grains 

 from ungerminated and germinating seeds of Indian corn. 

 In Fig. 3 it is seen that the grains have been much eroded 

 around the border and throughout their whole structure by 

 the action of the diastase. 



12. Circulation of Reserve Materials. — After the reserve 

 materials have been rendered soluble in the cell sap, and 

 diffusible through the cell membranes, they move from the 

 cells in which they are stored, by the processes of diffusion 

 (see page 36), to the growing regions of the embryo, there 

 to be used in part in the building up of new tissues, and in 

 part to be consumed by combustion or respiration. It is 



