Colorado Weed Seeds 
17 
endosperm, nucellus and seed-coats. The embryo (Fig. 5), or 
young plant, and consequently the most important structure of 
seed, upon reaching a certain stage in its development becomes 
dormant for a time, continuing its development only when condi- 
tions are again favorable for growth. In a well developed embryo 
three distinct parts can be found : Cotyledons, which supply food 
and in many cases become the first temporary leaves ; a hypocotyl, 
which terminates in the young root or radicle, and often pulls the 
cotyledons and plumule from the seed-coats; and the first bud or 
plumule. 
Fruit and Seed Distinguished. — The term seed is frequently 
and incorrectly applied to many of the small, dry, one-seeded, 
indehiscent fruits. The caryopsis or grain of wheat is known com- 
mercially as a seed as are the achenes of sunflower and rhubarb. 
A fruit is the matured ovary together with the seed or seeds. In 
the case of the one-seeded, indehis- 
cent fruits, the seed is enclosed in 
the ovary wall, which has become 
hardened, whereas a many-seeded 
dehiscent fruit such as the pea, has 
the ovary wall or pericarp repre- 
sented as the pod and the seeds are 
the enclosed “peas”. 
A caryopsis, (Fig. 6) such as the 
grain of wheat or of any other 
grass, is in reality a dry fruit con- 
taining one seed, and the fruit wall 
pericarp 
testn 
LcLllilllg LJllC dllVJ. XXC4.XV vv 
Fig. 6. Longitudinal section of ^ qnlit onen at maturitv tO 
a Caryopsis (Wheat) showing the QOeS noi spilL upcii 
pericarp and testa firmly grown ^IIqw the seed tO escape. Further- 
together. 
