126 



WHY DO SEEDS GERMINATE? 



castor bean. A section cut vertically through the castor bean 

 discloses a white oily mass directly under the seed coats. This 

 mass is called the endosperm. If it is tested with iodine, it will be 



found to contain 



.testa.. 



cot- 



starch; oil is also 

 present in consid- 

 erable quantity. 

 Within the endo- 

 sperm lies the em- 

 y^^&^ bl T > a thin > whitish 



asparagus "pine-- castor bean. "peanut structure. 



Seeds always contain a food supply which may be either in the coty- JYLOnOCOtyleClOnS > 

 ledons of the embryo or in an endosperm outside of the embryo. dicotvledotlS and 



polycotyledons. Plants that bear seeds having but a single cotyle- 

 don in the embryo are called monocotyledons. Although we find 

 many monocotyledonous plants in this part of the world, the group 

 may be said to be characteristic of the tropics. Sugar cane and 

 many of the large trees, such as the date palm, palmetto, and 

 banana, are examples. Among the common monocotyledons of 

 the north temperate zone are corn, lilies, grasses, grains, and 

 asparagus. 



Dicotyledons, or plants having two cotyledons in the seed, are 

 those with which we come in contact most frequently in daily 

 life. Many of our garden vegetables, peas, beans, squashes, 

 melons, etc., all of our great hardwood forest trees, beech, oak, 

 birch, chestnut, and hickory, the shade trees of our city streets, 

 elm, maple and poplar, all of our fruit trees, pears, apples, peaches, 

 and plums, and, in fact, a very large proportion of all plants 

 living in the north temperate zone, are dicotyledons. 



A third type of plant, with more than two cotyledons, is the 

 group called the polycotyledons, represented by the pines and their 

 kin. Such plants furnish most of the lumber and shingles used 

 in the construction of frame houses. The soft woods, as the pines, 

 hemlocks, spruces, and other " evergreens," are also of much 

 value in the manufacture of paper. The wood-pulp industry has 

 grown to such proportions as to be a menace to our softwood 

 forests. 



