556 



LIFE-HISTORIES 



"#^r*3;:; 



f-/-A 



Fig. 382. — Climbing Buckwheat {Polygonum Con rol cuius. Buckwheat 

 Family, PolygotiacecF) . Pistil (Y) during fertilization, cut vertically 

 to show stalk-like base (fs) of ovary; stalk of ovule (fu); end of stalk 

 (cha); the nucellus (nii), the micropyle, or opening to the nucellus {mi); 

 the inner integument (ii); the outer integument (ie); the embrj^o-sac 

 (e); nucleus of the embryo-sac (ck) ; the eg^-apparatus (t?) consisting 

 of three cells, the lower one being the egg-cell and the two others com- 

 panion cells which arc thought to represent rudimentary archegonia; 

 prothallial cells (an); style (g) ; stigma (».); 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 ogg-cell; here it discharges its (male) nuclcu.'^ which 

 fuses with the nucleus of the egg-cell and from this union an embryo 

 arises. (Strasburger.) — The plant is an annu;it \'ine rcsem1iling l^iuck- 

 whcat but with greenish flowers; native to JMimpc but a rimimon 

 weed in America. 



Fig. 383. — Shepherd's Purse (CapscUa Bursa-pastoris, Mustard Family, 

 Cruciferce) . Development of the embryo. A-D, successive stages, much 

 magnified, showing the suspensor (*'/), lc)wer end of embryo {h), cotyle- 

 dons (<:), 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. 



