THE ANGIOSPERMAE 



1595 



the base of the hypocotyl from which 

 the primary root, if present, or else 

 the first adventitious roots emerge 

 endogenously. An endogenous primary 

 root occurs in the dicotyledonous 

 Cinnamomutn, with, likewise, a coleo- B 

 rhiza. 



There are many anomalous seed- 

 ling structures and we can mention 

 only a few of the most striking. In a 

 few twining plants the twining habit 

 appears in the seedling, which grows 

 very rapidly, with very long inter- 

 nodes. An example of this is Physo- 

 stigma venenosiim, the Ordeal Bean. 

 A similar growth is seen in the climb- 

 ing parasite Cuscuta, whose seedling 

 consists only of a colourless filament, 

 bearing a few minute scales and no 

 trace of cotyledons, which acts as a 

 "seeker", growing freely and un- 

 attached along the ground until 

 it encounters a host plant, around 

 which it immediately entwines itself. 



Fig. 1455. — Zizania aquatica. Stages in 

 the development of the embryo to 

 illustrate the morphology of the 

 graminean embryo. The vascular 

 strands in black. Note that the 

 cotyledonary trace originates at the 

 base of the coleoptile and travels 

 downwards in the mesocotyl before 

 entering the cotyledon. {After La 

 Rue, Avery ond George.) 



The primary radicle is func- 

 tionless and soon aborts. 

 Absence of the cotyledons is 

 characteristic of several para- 

 sitic families, whose peculiar 

 germination methods will be 

 treated in Volume IV. 



If the Grasses have the most 

 Fig. i^s(y-—Odoutoghssum sp. A, Tuberous hypo- advanced seedlings among 



cotyl with rhizoids. B, First appearance of the MonOCOtyledoUS, the Orchid- 



plumule. 

 Burgfft'.) 



C, The first root appearing. (After 



aceae surely have the simplest, 



