CHAPTER II 

 GERMINATION 



30. Germination, botanically speaking, is the resump- 

 tion of growth by the dormant embryo or young plant 

 in the seed. Popularly it is the sprouting of seeds, the 

 first step in vegetation. To enable the seed to ger- 

 minate it must have a perfectly developed embryo, and 

 be mature or nearly so. It must not be too old for its 

 species (p. 49). It is complete when growth has rup- 

 tured the seed coats and the embryo has emerged. 



31. How seedlings grow. — Seedlings push through the 

 soil by the extension of their radicles or hypocotyls, 

 aided in some cases by their cotyledons. When the 

 descending parts have taken hold of the soil by means 

 of their root hairs, or by lateral root growth, upward 

 growth begins. Though in some cases (pea, oak, Fig. 

 13) the cotyledons descend, or at least remain beneath 

 the surface to help anchor the seedlings, they usually 

 "come up" above the surface (bean, radish), and often 

 turn green and perform the functions of true leaves 

 (maple, tomato, nasturtium). In the former case the 

 cotyledons contain large quantities of food which nourish 

 the plantlets ; in the latter the role of nurse is dropped 

 as soon as they turn green. Often while the first true 

 leaves are expanding, the roots contract and extend 

 laterally, thus drawing the little plants deeper in the soil 

 and anchoring them firmly. 



32. Growth in length is due to cell division and develop- 

 ment at the growing point ; that of girth, by cell division 

 and development of the cambium and contiguous cells. 



33. Hypocotyl or caulicle, the first internode or part 

 of stem below the cotyledons and above the radicle or 

 beginning of the true root. 



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