THE PEKIOD OF GREATEST ACTIVITY 49 



water. Because of this, good tilth is of vital importance since 

 firmness of the soil determines largely the ease with which the 

 planted seed secures this moisture. 



Absorption of Water by Seeds. — ^As soon as a seed is planted 

 in moist soil it begins to absorb water, and as a consequence, 

 it swells to its fullest extent before it germinates. Some seeds 

 absorb more than their own weight of water. When other con- 

 ditions are favorable, absorption of water determines largely the 

 welfare of the seedling and vigor in after-growth. The factors 

 which influence the rate of absorption are (a) contact between 

 the seed and the soil, (6) amount of moisture in the soil, (c) tem- 

 perature, and (d) salts. These factors may seem unimportant; on 

 the contrary they have direct bearing on successful farming. 



Contact between the seed and soil is the means whereby the 

 moisture in the soil gets to the seed. The better the contact, 

 therefore, the better the moisture supply for the seed, provided, 

 of course, there is moisture in the soil. This explains in part why 

 a firm seed bed is generally desirable. Alfalfa seed sown in a loose, 

 ashy seed bed very often results in failnre, because of the lack of 

 good contact between the seed and the soil. 



Moisture. — Seeds cannot germinate in dry soil. The planting 

 of soaked seeds in dry soil invariably results in failure. The more 

 water in the soil does not necessarily mean a more rapid absorption 

 and hence a more rapid germination. Too much water shuts out 

 oxygen and it also creates unfavorable temperature conditions. 



Wannth favors and cold retards absorption of water by seeds. 

 When water absorption is retarded germination also is retarded. 



Salts Retard the Rate of Absorption. — ^Under like condition 

 seeds will absorb moisture more slowly and hence germinate some- 

 what more slowly in a rich soil than in a poor one. If present in 

 considerable amounts, salts act as poisons. Many alkali soils 

 will not permit germination of seeds. Some salts are poisonous to 

 plants even in small amounts. Sometimes a farmer greatly retards 

 germination or even kills his corn seed, for example, by dropping 

 too much fertilizing salts on the seed in the hills or drills. 



THE VEGETATIVE OB GBOWING PERIOD 



The Period of Greatest Activity. — This is a most active period 

 in the life history of a plant. During this period the plant carries 

 on six distinct activities, namely: 

 4 



