GERMINATION 23 



43. The other set of organs is the essential part of the seed 

 and constitutes the germ or embryo. In the largest of the three 

 grand divisions of seed-bearing plants, the Dicotyledons, the 

 embryo consists usually of two symmetrical parts, the cotyle- 

 dons, which are connected by a third part — the caulicle. At 

 the end of the caulicle between the cotyledons there may also 

 be a minute structure, the plumule, which when well developed 

 shows clearly the outlines of one or more leaves in miniature. 



44. In another division of the seed-bearing plants there is 

 only one cotyledon, and hence the name applied to the group 

 is Monocotyledons. 



45. Besides the embryo there is frequently contained within 

 the seed coat a mass of food material for the use of the develop- 

 ing embryo. This food material, called endosperm or peri- 

 sperm, depending on the position it occupies in the seed, may 

 consist either of starch, proteid, oil, or cellulose, or a combina- 

 tion of two or more of these food principles. 



Germination 



46. The conditions necessary for the germination of seeds 

 are: First, a favorable temperature which might be designated 

 as warmth. The range and limits of this favorable temperature 

 are not sharply defined and may vary with the kind of seed. 

 Cold, a temperature below the Hmit within which germination 

 takes place, indefinitely retards development, though it does 

 not necessarily destroy the vitality of the germ if the seeds are 

 dry, while on the other hand, any considerable increase of 

 temperature above that of germination destroys all power of 

 further development. 



47. A second condition of germination is moisture. This 

 softens the seed coats, thus permitting the embryo to expand, 

 and also supplies the water which is everywhere necessary to 

 growth. 



