306 INTRODUCTION TO BOTANY 



which many asexual spores are formed. In both reproductive 

 and nutritive work the bryophytes are much more complex 

 than the thallophytes. 



The ferns have woody tissue and often have immense leaves 

 and are well equipped to do chlorophyll work. They often 

 store in one year food which serves in part for the growth of 

 the next year. Asexual spores are formed in great numbers 

 by means of highly specialized sporangia. These spores, when 

 they germinate (as in the case of the ferns studied), produce 

 chlorophyll-bearing, independent plants, which grow in obscure 

 places and produce sex organs by means of which sex spores 

 are formed. From the oospores new leafy fern plants grow. 



In the spermatophytes we have the most important and 

 most prominent plants of the earth. They have vegetative 

 structures that are very much more complex than are those 

 of any of the preceding groups. These vegetative structures 

 are so widely differentiated as to meet the demands of almost 

 any conditions. The flower and the seed are special reproduc- 

 tive structures which, with successful vegetative structures, 

 seem to have given these plants their position of ascendancy 

 in modern plant life. 



291. Classification. Throughout this book many illustra- 

 tions of the seed-plant group of the plant kingdom have been 

 used. Although but a few of these illustrations are cited 

 here, enough are given to enable the student to relate the 

 classification of spermatophytes to that of preceding groups. 



GROUP D. SPERMATOPHYTES 



CLASS I. GYMNOSPERMS. Genera used as illustrations Pinus (pine), 

 Picea (spruce), Juniperus (juniper), Sequoia (" big trees " and 

 redwoods) 

 CLASS II. ANGIOSPERMS 



SUB-CLASS I. MONOCOTYLEDONS. Genera used as illustrations 

 Lilium (lily), Zea (corn), Triticum (wheat), Avena (oats), and 

 many others 



SUB-CLASS II. DICOTYLEDONS. Genera used as illustrations 

 Quercus (oak), Capsella (shepherd's-purse), Pyrus (apple and 

 pear), Rosa (rose), and many others 



