NATURE AND STRUCTURE OF SEEDS 57 
On the surface of seeds occur certain structures which suggest 
the structural relation of the seed to the ovule. The micropyle, 
the small opening through which the pollen tube entered the 
ovule, persists as a tiny pit on the seed coat. Usually near the 
micropyle there is a much larger scar, called the hilum, left where 
the seed broke away from the funiculus, the stalk-like structure 
which attached the ovule to the ovary and through which the 
seed received food and water during its development. (Fig. 61.) 
In case an ovule turns over on its elongated stalk and grows fast 
to it, the stalk persists on the 
seed coat as a distinct ridge, 
called the raphe. (Fig. 62.) 
In some seeds, like those of 
Fic. 62. — A, seed of Pansy showing 
ws raphe (r). B, seed of Castor Bean show- 
Fic. 61.— Beans showing the ing caruncle (c). Cy, seed of White 
hylum at h and the micropyle Water Lily showing the aril or loose 
atm. jacket around the seed. 
the Castor Bean, an enlargement known as the caruncle develops 
near the micropyle. 
Structures such as hairs, plumes, hooks, and other appendages 
which do not occur on ovules, are direct outgrowths of the seed 
coat and function chiefly in dissemination. Similar appendages 
occur often on one-seeded ovaries in which case one can tell only 
by dissection whether the structure is a seed or one-seeded fruit. 
Many of the small one-seeded fruits are commonly called seeds. 
In addition to a seed, they contain the ovary wall which persists 
as an outer covering over the seed. The so-called seeds of Let- 
tuce, Buckwheat, Ragweed, and the grains such as Corn, Wheat, 
Barley, Rye, and Oats are familiar examples of one-seeded fruits 
which are commonly called seeds. While they are not identical 
with true seeds in structure, they are in function and therefore 
may be appropriately discussed with seeds. In these one-seeded 
fruits, the seed is protected by the hardened ovary wall, and 
consequently, the seed coat is poorly developed, forming only a 
