CHAPTER VI 



DEVELOPMENT 



§ I. Vitality of Seeds. § 2. Dormancy of Seeds. § 3. Viviparous Seeds. 

 § 4. Germination — Conditions. § 5. Germination — Liberation of 

 .the Embryo. § 6. Germination — Emergence of the Seedling. § 7. 

 Mode of Growth. § 8. External Conditions and Growth. § 9. 

 Development — The Vegetative Phase. § 10. Seasonal Changes, 

 Protection, and Rhythm. § 11. The Reproductive Phase. § 12. 

 Senescence, Death, and Individuality. 



§ I. Vitality of Seeds 



The seed, when it is ripe and becomes separated from the 

 parent plant, characteristically contains an embryo in which 

 marked differentiation has taken place. Radicle and 

 cotyledons are present, together with a stem growing-point, 

 which may have already given rise to an axis with several 

 leaf rudiments — the plumule. In the final stages of its 

 formation the seed has lost much water, so that it may 

 contain only about 10 per cent. ; sap is no longer present 

 in the vacuoles, and in this condition chemical reactions, 

 even respiration, are reduced to a minimum. In ordinary 

 air, which is not very dry, many seeds continue to respire 

 very slowly, giving off small amounts of carbon dioxide. 

 According to White (1909) the wheat is an example of 

 such a seed, while the oat does not respire appreciably. 

 When seeds are specially desiccated respiration almost 

 always ceases. In such seeds, and in those stored in 

 absence of oxygen, slight anaerobic respiration may go on. 

 Becquerel (1907) has shown that some seeds may be 

 desiccated and kept in a vacuum for two years without 

 losing their vitality. It is the essence of the seed's power 

 of rest that reaction is reduced almost to the vanishing point. 



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