CHAPTER XXXIV 

 GROWTH, DORMANCY, AND GERMINATION OF SEEDS 



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From the child who is thrilled by the story of Jack's miraculous beans 

 that grew to sublime heights in a single night, to the world tourists who 

 are perennially duped by the peddlers of Egypt with their living grains 

 of wheat allegedly taken from the tombs of the Pharaohs, most persons 

 are curious about how long seeds remain alive, why some seeds germi- 

 nate readily and why the seeds of other equally common plants fail to 

 germinate within a few weeks although the embryo appears to be in 

 perfect condition. These phenomena have been studied experimentally 

 in recent years and some of the results will be discussed in this chapter. 



From zygote to mature embryo. The germination of the zygote is the 

 beginning of the development of the embryo of a new plant similar in 

 most respects to that in which the zygote was formed. Through cell 

 division and some enlargement the embryo soon consists of a small body 

 of meristem cells. In seeds of some plants, such as those of orchids, de- 

 velopment of the embryo ceases at this early stage. In seeds of most 

 plants, however, cell division, enlargement, and differentiation continue, 

 and an embryo with well-defined cotyledons, hypocotyl, and plumule 

 results. This development of the embryo of a seed plant occurs inside 

 the ovule. Meanwhile the ovule coats grow and become seed coats. The 

 nucellus also grows in the seeds of a few kinds of plants, but in most 

 seeds it either becomes a negligible structure, or is entirely destroyed by 

 the growth of the other seed structures. 



The growth of the embryo is thus definitely limited by the tissues that 

 enclose it. As its supply of water and oxygen decreases, and the dead 

 seed coats prevent further expansion, the embryo ceases to grow and 

 becomes dormant. 



If the young embryos are removed from the ovules and placed in a 

 sterile culture medium containing inorganic salts, water, and sugar, with 

 oxygen available, they do not become dormant but continue to grow as 

 seedlings. When the immature embryos of certain varieties of peach are 

 planted under these conditions the plants are better than those that 



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