320 MORPHOLOGY OF THE ANGIOSPERMS 



or may be a renewal after dormancy for various periods, up to more 

 than a year following seed shedding. Intraseminal growth, so far as 

 known, seems to be restricted largely to the more primitive taxa and to 

 herbaceous, geophilous genera. 



After-ripening of the epicotyl in the seedling stage, after hypocotyl 

 and radicle are developing, has received some attention. But this is not 

 akin to after-ripening of the embryo in the seed; it is related to the 

 dominance of growth activity elsewhere in the seedling — the elabora- 

 tion of the cotyledons as foliage organs; the establishment of a root 

 system; in some genera, the storage of food in the hypocotyl. 



There is need for much more information concerning the later stages 

 of embryo development. Studies of dormancy and after-ripening should 

 include the full story of embryology. Hidden morphological changes 

 may play important parts in the story of germination. 



Germination 



The bursting of the seed coats in germination results from the en- 

 largement of the embryo, either throughout, or restricted to definite 

 parts. The term epigeal is applied to germination where the seed coat 

 is carried up into the air, regardless of place where germination begins 

 (seeds on the surface of the soil or somewhat below may be carried up 

 into the air); the term hijpogeal, where seed coat and cotyledons re- 

 main in the soil. Differences between the epigeal and hypogeal methods 

 of germination and early seedling development are generally great, 

 though transitional conditions are frequent; the hypogeal method is 

 clearly advanced. Most dicotyledons (like the gymnosperms) are epi- 

 geal; monocotyledons are largely hypogeal. The papilionaceous legumes 

 show many transitional forms. 



The root system varies greatly in time and vigor of development in 

 both types of germination. In epigeal germination, tlie root tip and 

 hypocotyl commonly grow rapidly; theii- elongation pulls the cotyledons 

 from the seed coats. Exceptions, where the main root grows little or 

 not at all, are occasional — Semperviviim, PhijUodoce, Anemiopsis. In 

 these forms and in those monocotyledons in which the main root is 

 weak or does not develop, the first root hairs form a crown at the base 

 of the hypocotyl. In hypogeal development, the main root usually de- 

 velops rapidly and becomes thick and strong. The taxon "Megarrhiza" 

 of Darwin and Asa Gray was based on possession of development of 

 this type. Root hairs are abundant on the roots from earliest stages. 

 Here belong the Fagaceae, Nymphaeaceae, Juglandaceae, Hippocasta- 

 naceae. In the monocotyledons, several types of germination have been 

 distinguished. In the majority of taxa — Palmae, the advanced Liliaceae, 

 Amaryllidaceae — the root tip appears very early, and the root develops 



