PARTS OF SEEDS: CONCLUSIONS 17 



etc., the food is stored up in the two first seed leaves (cotyledons) 

 which make the bulk of the embryo and are easily recognized as 

 the two fleshy halves. In other seeds, as in the castor bean, the 

 corn, wheat, etc., the food is stored around, or at one side of the 

 embryo, within the seed coats, and is then known as endosperm 

 (literally the inside of the seed). 



22. Conditions of germination of seeds. In order that the 

 seeds of plants may germinate, certain conditions must be ful- 

 filled. First, the seed must be good; i.e., it must meet certain 

 internal conditions, as to maturity, age, and the vitality of the 

 embryo. Second, the external conditions must be favorable. 

 Seeds vary a great deal as to their germination according to age, 

 etc. ; some seeds must first pass a resting period of several weeks 

 or months before they will germinate. For most seeds there are 

 three external conditions which must be present in order that 

 they may germinate; air, a suitable amount of moisture, and a 

 suitable degree of warmth. In the absence of these conditions the 

 seeds remain dormant for a period of time ranging from a very 

 few days in the case of some kinds to many years in the case of 

 others. If the seed is dry, it will resist great extremes of cold 

 (many degrees below freezing) and warmth. If the seed is moist 

 it will resist these extremes for a shorter period. Extreme cold 

 prevents or retards germination of the seed. Growth begins 

 slowly at about 6 C. (about 43 F.), and increases with the ele- 

 vation of the temperature up to an optimum, which is often dif- 

 ferent in different plants, and then decreases with higher tem- 

 peratures until at a maximum temperature growth ceases. Ger- 

 mination may begin in the absence of air (of oxygen) but soon 

 ceases.* 



* In the practical work exercises can be arranged to demonstrate the 

 influence of these conditions on germination. 



