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- FIG. 71. a, 

 minous seeds. Among Monocotyledons albumi- Pine 



nous seeds prevail, while both types are about 



,, ,^.. , ! , 



equally common among Dicotyledons. 



seed sec- 

 lengthwise 

 to show polycot- 

 ledonv b Pine 



Resting Period, Vitality, and Longevity of Seeds ^ man^oty^e- 

 The function of a seed as the plant's organ of dons becoming 

 dissemination depends upon a number of physi- f 

 ological features, of which the chief one is the enlar ed 

 ability of the seed to remain alive with the ordi- 

 nary life processes so slowed that they seem not to be taking 

 place at all. 



Resting Period. The resting condition is a valuable physio- 

 logical feature to the seed, because in this condition the embryo 

 can endure cold, heat, dryness, intense light, and various other 

 conditions to which the seed is exposed during dissemination. 

 How the resting condition is brought about and how it is main- 

 tained, often many years, are not thoroughly understood. The 

 resting condition is associated with dryness, a condition obtained 



