12 GROWTH AND WORK OF PLANTS 



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

 (literally the inside of the seed). 



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

 seeds of plants may germinate, certain conditions must be fulfilled. 

 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 viability 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 germi- 

 nate; 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 elevation of the tempera- 

 ture up to an optimum, which is often different in different plants, 

 and then decreases with higher temperatures until at a maxi- 

 mum temperature growth ceases. Germination 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. 



