THE VARIETY OF PLANT LIFE 



103 



dry, conspicuous or small, to protect the seed and aid in its 

 dispersal. As a convenience in classifying this large assemblage of 

 species, Angiosperms are customarily subdivided into two sub- 

 classes on the basis of reproductive and vegetative differences. 

 One sub-class is known as the dicots, since there are two cotyle- 

 dons in the seed (see p. 75); but plants belonging to this sub- 

 group also have other features in common. Their flowers usually 

 have the petals, sepals and stamens in fours or fives; their leaves 









Fig. 72.- 



-Monocots, such as corn, have pithy stems with scattered bundles of 

 conducting cells. 



are usually broad and netted-veined ; and their stems are capable 

 of producing wood and annually increasing in diameter, forming 

 annual rings (fig. 71). The other sub-class — the monocots — in- 

 cludes those species with a single cotyledon in the seed; leaves 

 that are usually long, slender and parallel-veined; flower parts 

 in threes or sixes; and pithy stems lacking the ability to increase 

 annually in diameter (fig. 72). 



The DICOTS are considered by most botanists to be more 

 primitive than the Monocots, and to represent simpler stages in 

 floral evolution. This sub-class is made up of 100,000 to 125,000 



