ANGIOSPERMS 237 
from the peculiar character of their embryos. In one 
division the root is developed at one end of the embryo 
and the single cotyledon at 
the other end, the stem 
coming out on one side. In 
the other division the root 
is developed at one end of 
the embryo and the stem at 
the other end, two cotyle- 
dons coming out on oppo- 
site sides just behind the ‘ 
stem tip. Therefore, the Fic. 228.—Seed of violet, one figure show- 
ee ep é ing the hard testa, the other the em- 
first division is called Mono- bryo (young sporophyte) that has 
cotyledons (one cotyledon), oe from the odspore.—After 
AILLON. 
and the second is called Di- 
cotyledons (two cotyledons). There are many other differ- 
ences between Monocotyledons and Dicotyledons, but this 
difference between the embryos has been selected to form 
the names. 
The embryos of Angiosperms differ much as to the com- 
pleteness of their development within the seed. In some 
plants the embryo is merely a mass of cells, without any 
organization of root, stem, or leaf. In many plants, on 
the other hand, the embryo becomes highly developed, 
showing all the principal organs and the plumule con- 
taining several well-organized young leaves (Chapter V). 
142. Seed.—The seed is evidently an ovule (sporangium) 
containing a female gametophyte which has developed a 
new sporophyte (embryo). This complex structure is 
invested by the hard seed-coat, and is a protected resting 
condition of the plant. 
The seed-coat (testa) in Angiosperms is exceedingly 
variable in structure and appearance. Sometimes it is 
smooth and glistening, sometimes pitted, sometimes rough 
with warts or ridges. In many cases prominent append- 
