506 
Fic. 
Fig. 
LIFE-HISTORIES 
382.—Climbing Buckwheat (Polygonum Convolvulus, Buckwheat 
Family, Polygonacee). Pistil (48) during fertilization, cut vertically 
to show stalk-like base (fs) of ovary; stalk of ovule (fu); end of stalk 
(cha); the nucellus (nw), the micropyle, or opening to the nucellus (mz); 
the inner integument (77); the outer integument (ie); the embryo-sac 
(e); nucleus of the embryo-sac (ek); the egg-apparatus (e7) consisting 
of three cells, the lower one being the egg-cell and the two others com- 
panion cells which are thought to represent rudimentary archegonia; 
prothallial cells (an); style (g); stigma (n); pollen grains (p); and 
pollen-tubes (ps). A pollen grain falling upon the stigma produces a 
tube which grows down through the style, enters the micropyle, and 
penetrates to the egg-cell; here it discharges its (male) nucleus which 
fuses with the nucleus of the egg-cell and from this union an embryo 
arises. (Strasburger.)—The plant is an annual vine resembling buck- 
wheat but with greenish flowers; native to Europe but a common 
weed in America. 
383.—Shepherd’s Purse (Capsella Bursa-pastoris, Mustard Family, 
Crucifere). Development of the embryo. A-—D, successive stages, much 
magnified, showing the suspensor (et), lower end of embryo (h), cotyle- 
dons (c), and the stem-tip (p) from which the plumule arises. (Han- 
stein.)—The plant is annual, about 50 cm. tall, with small white flowers 
and dry fruit; native of Europe; common as a weed in America. 
