368 TEXTBOOK OF BOTANY 



seed coats. The embryo consists of a hypocotyl, a plumule, and two 

 large, greatly thickened cotyledons. All the accumulated food in a 

 bean seed is in the embryo. The seeds of many other plants, such as 

 species of legumes, mustards, hickory nuts, and pumpkins, also lack 

 endosperms. 



The grain of corn, like that of wheat, consists of a grain coat, a large 

 endosperm, and an embryo, which is near the inner end of the seed. 

 There is a single large cotyledon (scutellum) more or less enclosing 

 the hypocotyl and the plumule (Fig. 113). Because of the fact that the 

 corn grain develops from both the ovule and the ovularv wall, it is really 

 a fruit. The grain coat is composed of seed coats plus the adhering 

 ovulary wall, or pericarp. 



Monocots and dicots. From our early study of the vegetative organs 

 of a plant we learned that monocots and dicots may be recognized partly 

 bv the venation of the leaves and the arrangement of the vascular bun- 

 dles in the stem. The Hower parts of monocots are often in 3's or 6's, 

 while those of dicots are often in 4's or 5's or in some multiple of these 

 numbers. The terms refer, however, to the number of cotvledons" in the 

 embryo of the seed. The seeds of bean, squash, apple, and ash, along 

 with many others, have two cotyledons, and these plants are called 

 dicots; the seeds of wheat, corn, rye, and other grasses contain but one 

 cotyledon, and such plants are monocots. 



Gymnosperms and angiosperms. Conifers, such as pines and spruces, 

 bear seeds on the upper sides of overlapping scales arranged in a cone. 

 The seeds are not enclosed by the scales but are exposed on their flat 

 open surfaces. Plants bearing seeds in this manner are termed gymno- 

 sperms ( "gymnosperm" means "naked seed"). Most seed plants have 

 carpels united in the form of a distinct pistil. The seeds enclosed in the 

 ovulary of the pistil are covered, or "hidden"; hence the name, angio- 

 sperms. 



Dissemination of seeds. When seeds are mature they may become 

 separated from the fruit or the parent plant in several ways. The seeds 

 mav be expelled from fruits such as legumes and capsules when the 

 ovulary walls dry out, twist, or curl and shrink. The one-seeded fruits, 

 such as the akene and the grain, become free b\' abscission from the 

 receptacle. The seeds in many fruits, such as those in pomes, nuts, 

 drupes, and berries, are set free only by the decay of the fruit. 



2 "Monocots" and "dicots" are abbre\iations now in rather general use for the longer 

 terms "monocotyledons" and "dicotyledons." 



