THE SEED PLANTS 303 
While these developments have been taking place in the 
embryo sac, the integument walls have become dry and hard, 
so that, by the time the young plant has differentiated the 
root, stem, and leaf regions, it is usually inclosed by hard 
and dry walls, and the whole structure is a seed. In some 
cases the seed is dropped 
from the parent plant at 
once, and may begin its 
growth immediately. Seeds : 
may lie dormant on the - oa ae str 
ground until the return = 
of spring, or may in some 
rr 
cases lie dormant for sev- 
eral years, and still retain ne 
their vitality. The seeds of 
the cocklebur and of some eae 
desert plants may lie in the 
ground for several years ~-inint 
and then grow. The seed 
--ou int 
coats sometimes become so 
dry and hard that the water 
and air necessary for ger- 
mination cannot penetrate, Fic. 232. Diagram of the ovule, embryo 
and this condition remains *2% and embryo of the shepherd’s-purse 
until, through decay of the ciao iniesieiinge 
re The parts shown are the outer integument 
wall or through injury tO (ou int), inner integument (in int), embryo- 
it, the needed materials can sae wall (¢ s w), suspensor cells (susp c), 
get into the seed. Most Sat a ee a the oad 
seeds, such as wheat, corn, 
and oats, lose their vitality within a few years at the most. 
288. The fruit. The relations between seed and fruit are 
not easily defined, for the reason that the fruit may include 
a few or many structures. The ripened ovule containing the 
embryo is the seed. Sometimes structures other than the seed 
ripen with it; regardless of how many things ripen with the 
seed, all are included in the term fruit. In the sunflower the 
