CHAPTER XXXVII. 

 ANGIOSPERMS.* 



553. General characters. The Angiosperms include the 

 members of the second class of seed plants (Spermatophytes). 

 They are distinguished from the members of the first class, the 

 Gymnosperms, chiefly for two reasons. First, the seeds are 

 enclosed in a vessel or case. This vessel or case is formed from 

 the ovary (an ovule case), sometimes with the cohesion also of 

 other parts of the flower (Chapter XXII) . Second, the presence of 

 the true flower,^ usually with a perianth (see Chapters XVIII, 

 XIX) . The plants (which are sporophytes) are adapted to live 

 under a great variety of conditions both in water and on land. 

 There is also a great variation in size, from large tall trees to the 

 shrubs and herbs, some of which are quite minute. The leaf is 

 typically a thin, expanded structure, but varies in plants living 



To THE TEACHER. The first part of this chapter is presented here as a 

 brief text review of some of the work in Part I. The most of the chapter 

 is too technical for any but advanced students, and is included here to round 

 out the text and sum up the brief discussions in former chapters of develop- 

 ment, alternation of generations, life histories, etc. 



* Since members of the Angiosperms were chiefly used for the study of 

 seeds, the different parts and functions of the plant, this chapter will be 

 treated more'in the nature of a brief review and in pointing out the position 

 of the different parts in the life cycle when compared with the other groups 

 of plants. 



f The aggregation of sporophylls along an axis in the higher Pteride- 

 phytes and in the Gymnosperms is sometimes spoken of as a primitive 

 flower. But the " flower " axis is elongated, the members are in spirals, 

 and there is an absence of a perianth of brightly colored members. In a few 

 of the lower Angiosperms some of the members of the flowers are in spirals. 

 In the magnolias and tulip tree (Liriodendrori) the axis of the flower is con- 

 siderably elongated, and it is believed to represent a primitive condition. 

 But there is a highly developed perianth. 



405 



