SECT. II 



PHANEROGAMIA 525 



are found, and in the genus Phaseolus, Ph. indgaris is epigeal and Ph. 

 multifionis hypogeal. 



The germination of monocotyledonous seeds differs from the cases 

 described above in that after the main root has emerged — sometimes 

 before this — the sheathing base of the larger or smaller cotyledon 

 emerges from the seed. Its tip remains either for a time or permanently 

 in the seed, and serves as an absorbent organ to convey the reserve 

 materials stored in the endosperm to the seedling. The first leaf of the 

 latter soon emerges from the sheathing base of the cotyledon (Fig. 494). 

 IndiA'idual peculiarities cannot be described here, but it may be men- 

 tioned that very hard seed-coats are often provided with special 

 arrangements to enable the root to escape. Thus in the coco-nut 

 three openings are present, one corresponding to each carpel. The 

 opening behind which the tip of the root of the single embryo is 

 situated, is covered by a very thin layer, Avhile the two other openings 

 are firmly closed. The hard stony seed-coat of another Palm 

 (Acrocomia sdcrocaiya) (Fig. 495) has a loosely fastened plug opposite 

 the tip of the root. In the whole family of the Scitamineae there is 

 a limited thinner region of the hard seed-coat above the root-tip of 

 the embryo, which is lifted up as a sort of lid on germination. 



The so-called " viviparous " plants show peculiar arrangemeuts ^¥hich can only 

 be briefly mentioned here. Vivipary (^^) is found exclusively in the inhabitants 

 of tropical mangrove-swamps and is to be regarded as an oecological adaptation to 

 the conditions of life. The one-seeded fruits germinate while still attached to the 

 parent plant, i.e. the pericarp is ruptured by the radicle of the embryo which first 

 grows from the micropylar end of the seed. The hypocotyl which thus becomes 

 free may attain the length of over 1 metre in Rhizojphora. This swells some- 

 what in the lower part, and the embryo thus hangs by its absorbent cotyledons 

 which remain in the seed, until it separates from the plant owing to its own weight, 

 and, falling vertically, sticks into the soft mud. The various genera of Rhizo- 

 phoraceae (Figs. 496, 653) and the biologically similar Avicennia, Aegiceras, and 

 Carapa show various degrees of vivipary. One of the smallest examples from the 

 family of the Rhizophoraceae is represented in Fig. 496. 



SPECIAL PART i}'^) 



Arrang-ement of Classes, Orders, and Families 



It has been mentioned in the introductory portion of this section, 

 and again in speaking of the floral relations and the developmental 

 history of the sexual generation, that the Gymnosperms are phylogeneti- 

 cally more ancient than the Angiosperms. For this reason the 

 Gymnosperms are placed first. The long-disputed question as to 

 whether tlie Monocotyledons or Dicotyledons are the more primitive 

 is perhaps settled by the durivation of the Monocotyledons from the 

 Polycarpicae among the Dicotyledons ; these exhibit features of agree- 



