18 GERMINATION OF THE SEED 



fulfilled or no growth will result. If seeds are kept dry, even 

 though they may be in a warm place and surrounded by 

 air which contains all the oxygen ever needed by plants, 

 they will not sprout. They will, however, retain their 

 vitality for a long time, several years being the ordinary 

 maximum, although some seeds have grown after being 

 kept fifty or one hundred years. So also, if seeds are placed 

 in water freed from air, and kept warm, no germination 

 results, because the water prevents oxygen from reaching 

 the seed. Under these conditions, however, seeds will decay 

 in a short time, due to the influence of bacteria which 

 act in the presence of moisture, but not otherwise. This 

 indicates the importance of planting seeds in aerated soil, 

 not in soil saturated with water. Seeds under the latter 

 condition will decay. And finally if seeds are supplied with 

 sufficient moisture and are well aerated, but kept cold, no 

 germination will occur. It is absolutely necessary that there 

 be present sufficient water, oxygen, and heat. 



2. Water. — The food material packed away in the 

 cotyledons or endosperm is anhydrous and insoluble. To 

 be transported from the cells in which it is stored to the 

 growing root and plumule where it can be used in manufac- 

 turing new cells, this food material must be changed to a 

 soluble form. The chemical change which makes starch, 

 oil, and protein soluble is hydrolytic in character; that 

 is, water is necessary to break down the insoluble mole- 

 cules of stored food into soluble molecules of transportable 

 food. Certain catalytic agents or enzymes are necessary 

 for this hydrolytic action. There must be in addition 

 enough water to dissolve the soluble compounds, and to 

 keep the new cells properly distended as fast as they are 

 formed. 



A seed in the air dry condition contains about 10 per cent, 

 of water, but to start germination there must be present 

 about 30 per cent. The water is imbibed in part through 

 the seed coat, but mostly through small openings where the 

 seed was attached to the parent plant and adjacent to the 

 embryo. This absorption or imbibition of water is apparently 

 caused by an attraction which the contents of the seed have 



