RESTING PERIOD 



67 



such as Peas, Clover, Alfalfa, Tomatoes, Melons, Cotton, Fruit 

 trees, and many forest trees are Dicotyledons. Each of these 

 classes includes a large number of important cultivated plants as 

 well as many that are regarded as weeds. 



Since the classification into Monocotyledons and Dicotyledons 

 applies only to the Flowering Plants, such plants as the Larch, 

 Pine, Spruce, Fir, Hemlock, which belong to the 

 Gymnosperms where there are no true flowers, 

 are omitted in this classification. The seeds of 

 a number of the Gymnosperms commonly have 

 more than two and those of the Pine and Cypress 

 commonly have many cotyledons. (Fig. 71.) 

 They are polycotyledonous seeds and the plants 

 may be described as Poly cotyledons. 



The difference in the location of the stored 

 food in seeds serves in distinguishing them but 

 does not affect their function or commercial 

 value. In all types of seeds, the endosperm 

 must be absorbed by the cotyledons before it is 

 available for the growth of the embryo. This 

 absorption occurs before germination in the ex- 

 albuminous seeds but during germination in albu- 

 minous seeds. Among Monocotyledons albumi- 

 nous seeds prevail, while both types are about 

 equally common among Dicotyledons. 



a 



Fig. 71. — a, 

 Pine seed sec- 

 tioned lengthwise 

 to show polycot- 

 yledony. 6, Pine 

 seed germinating, 

 the many cotyle- 

 dons becoming 

 free from the seed 

 coat. Both are 



Resting Period, Vitality, and Longevity of Seeds 



Most seeds, after they complete their develop- 

 ment, dry out and pass into a state of dormancy. 

 The dormant period, known as the resting 

 period, varies greatly with different seeds, rang- enlarged. 

 ing from a few days to months or years. When seeds are to be 

 used for growing new crops, one must consider their resting 

 period, vitahty, and longevity. 



Resting Period. — While seeds are being scattered from the 

 mother plant and are awaiting favorable conditions for germina- 

 tion, they are commonly exposed to adverse conditions, such as 

 cold, heat, dryness, intense light, etc. In the resting condition, 

 with life processes reduced to a minimum of activity, seeds have 

 remarkable endurance and are thus able to endure without injury 

 conditions that would quickly kill them if they were active. 



