SEEDS AND SEEDLINGS 



139 



moisture, or, in such hard-shelled seeds as the coconut, hick- 

 ory nuts, walnuts, and butternuts, there must be a thin or 

 soft-walled place tlirough which water can enter. Usually the 

 little opening in the ovule, 

 known as the mieropyle (Fig. 

 109, to), remains in the seed 

 and serves to admit moisture. 



The coats of many seeds 

 have wings or outgrowths of 

 hairs which aid in their dis- 

 persal, as already mentioned. 

 Other modifications in the 

 coats of seeds apparently, in 

 some cases, serve as aids in 

 their dispersal, and others as 

 means of preventing the seed 

 from being eaten by animals. 



130. Conditions for germi- 

 nation. A sound, live seed will 

 germinate or sprout when suit- 

 able conditions are present. 

 The requisites for germina- 

 tion are : 



(1) The proper tempera- 

 ture. 



(2) Enough moisture. 



(3) Air or oxygen.^ 



The temperature most fa- 

 vorable for germination varies 

 with the kind of seed ; for any given kind there seems to be 

 a lowest limit, a most favorable (optimum) temperature, and a 

 highest limit. The approximate temperatures for a few species 

 are given on the next page (in Fahrenheit degrees).^ 



1 Some seeds begin to germinate without air, but soon die unless it is 

 supplied to them. 



2 See Detmer, Keimungsprocess der Samen, chap. iii. 6. Fischer, Jena. 



Fig. 129. Lengthwise section (some- 

 what diagrammatic) through the em- 

 bryo end of a grain of wheat 



en, endosperm ; sc, scutellum, or absorh- 

 ing portion of cotyledon; c.t, cellular 

 tissue (containing much oil) in which the 

 cotyledon is embedded ; v.c, vegetative 

 cone or growing point ; h, hypocotyl ; 

 r.c, rootcap; per, periderm, or coating 

 of grain ;/, scar to which the funiculus or 

 seed stalk was attached. AfterWarming. 

 Magnified about 26 diameters 



