STEMS IN THE CLASSIFICATION OF SEED PLANTS 183 



51. Stems in the Classification of Seed Plants. — The 



scientific name for all plants which produce seeds is sper- 

 matophytes, a word whose first part means seed and whose 

 last syllable means plants. 



The spermatophytes are composed of two great groups, 

 the gymnosperms and the angiosperms. The word gym- 

 nosperm means naked-seed; the word angiosperm means 

 seeds-in-a-box. Pines and other common northern ever- 

 greens are gymnosperms ; all other common plants which 

 produce seeds are angiosperms. From a ripe pine-cone you 

 can shake out the naked seeds ; all other seeds are inclosed 

 within the structure called ovary (see page 60). The 

 ovary usually develops into what we call fruit. In some 

 angiosperms, Uke corn, the seed case or ovary seems like 

 the outer part of the seed itself, but in origin it is perfectly 

 distinct from the seed. 



The angiosperms are composed of two great divisions of 

 plants known as monocotyledons and dicotyledons. Mono- 

 cotyledon means one cotyledon; dicotyledon means two 

 cotyledons. Cotyledons, as you know, are parts of the 

 embryo. Your attention has already been called to the 

 fact that plants like corn have but one cotyledon, and 

 that the bean is an example of plants with two (see 

 page 66). 



It is evident that this classification of seed plants is not 

 based upon differences in their stem structures. It is based 

 rather upon the way the seeds are borne and upon the 

 number of cotyledons ; the meanings of the names used 

 indicate that such is the basis. As a matter of fact, in 

 deciding what the great subdivisions of plants are, bota- 

 nists do not depend upon single characters to guide them. 

 The great groups of plants are based upon similarities or 



