THE ANGIOSPERMAE 



1577 



germination of which only a few can be mentioned. The seeds of some 

 monocotyledonous famihes have an opening in the testa, over the place 

 at which the radicle will emerge, which is closed by a hard plug against 

 which the radicle pushes at germination. These are found in the Zingi- 

 beraceae, Marantaceae and Musaceae, the plug being formed by an aril. 

 Similar " seed-lids " occur in the Commelinaceae, Potamogetonaceae, and 

 Lemnaceae. Among Dicotyledons, the genus Sorbiis also has a kind of 

 " lid " opposite the radicle, which the latter carries with it, on germination, 

 as a temporary root cap. 



Hill investigated the mode of germination in a number of cases where 

 the seeds remain enclosed in a stony endocarp, which is often very hard. 



Fig. 1^27.— Phoenix dactylifera. Date Palm. Germination. I. Seed in longitudinal 

 section. II. Seed in transverse section (E = embryo). III. Germinating seed in 

 longitudinal section showing the great development of the haustorial cotyledon. 

 IV. The same in transverse section. V and VI. Two aspects of the embryo. 

 {From Troll, "Vergleichende Morphologie der hoheren Pftanzen\) 



