DIV. n SPERMATOPHYTA 589 



This most frequent type of germination is characterised by the cotyledons 

 being expanded above ground and is termed EPIGEAL. It is nearly always found 

 in the case of small seeds. 



HYPOGEAL germination is for the most part found in large-seeded Dicotyledons, 

 the cotyledons of which contain the stored reserve materials (e.g. Vicia, faba, 

 Pisum, Aesculus, Juglans, etc.). It is characterised by the cotyledons remaining 

 enclosed in the seed-coat after the root has penetrated into the soil ; the epicoty- 

 ledonary stem emerges from between the cotyledons, becomes erect, and bears the 

 later leaves in the usual way. While there is a sharp morphological distinction 

 between the two types of germination, the difference is of little systematic value ; 

 within the Papilionaceae many intermediate conditions are found, and in the 

 genus Phaseolus, Ph. vulgaris is epigeal and Ph. multiflonis hypogeal. 



The germination of monocotyledonous seeds differs from the cases described 

 above in that after the main root has emerged the sheathing base of the larger 

 or smaller cotyled*on 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. 579 b}. 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, while the two other openings are 

 firmly closed. The hard stony seed -coat of another Palm (Acrocomia sderocarpa) 

 (Fig. 580) 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 arrangements which can only 

 be briefly mentioned here (Fig. 581). Vivipary is found in the inhabitants of 

 tropical mangrove-swamps and is to be regarded as an ecological 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 Rhizophora (cf. Fig. 716). This 

 swells somewhat 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. 



Arrangement of the Classes, Orders, and Families 

 CLASS I 



Gymnospermae ( 14 ) 

 Order 1. Cycadinae 



This includes the single Family Cycadaceae. These are woody plants 

 restricted to tropical and sub-tropical regions. Cycas is a native of Asia ; 

 Macrozamia and Bowenia of Australia. Encephalartos and Stangeria are African, 

 while America has the genera Dioon, Ceratozamia, Zamia, and Microcycas. The 

 stem, Avhich undergoes secondary growth in thickness, is as a rule unbranched or 

 forms a sympodium, and bears large, pinnate foliage leaves. These, which are 



