282 



PLANT LIFE. 



vided to recei\-e it. The wall cell remains undivided and 

 grows to form an unseptatc filament, called the "pollen 

 tube" (fig-s. 317, 31S, 319, 321, 322, 323). In gymno- 



FlG. 314. 



Fig. 315 



Fig. 314. — Vertical median section of the mature spermary of a fern {Ad iauiu )}t 

 capillus-vciicris). /, adjacent cells of gainetophyte (tigs. 74, 77) ; a, spermarj', show- 

 ing wall composed of three cells, the two lower ('abo\'e and below letter a) being ring- 

 like. The chloroplasts have accumulated on the inner face. The interior cell, origi- 

 nally single, has di\'ided into a number, the sperm mother cells, which at this stage are 

 loosened and contain each a fully de\'eloped coiled sperm. Magnified 550 diam. — 

 After Sachs. 



Fig, 315. — -A vertical median section of the gametophyte of Sclai^iuelia sioloinfera. 

 />, a single cell representing the vegetative part of the gametophyte (compare tigs. 74, 

 314) ; 71:', the cells forming the wall of the spermary ; s, the mother cells of tlie sperms, 

 each containing one sperm and now loosened from each other. The gametophyte with 

 its single spermary scarcely exceeds the size of the microspore which produces it and 

 therefore only just bursts the outer wall of the spore. The solution of the wall cells 

 7L' allows the sperms to escape. Magnified ''140 diam. — After Strasburger. 



Fig. 316.— Diagram of the gametophyte of the larch {f^arix Eu7-opa;a), formed in the 

 microspore. /, the vegetative cell ; st, two stalk cells of the sperman,' ; -v. cell whose 

 nucleus subsequently di\'ides to form two sperms (the walls of the mother cells not 

 forming) ; iv, t)ie uall of tiie spermary which remains undi\'ided. Conii.iare hg. ^^15. 



sperms this penetrates the megasporangium (o\-ulc bodv) and 

 reaches the female gametophyte on whose surface are formed 

 the ovaries (figs. 319, 320, 321, 322 ). In the course of its 

 development the S])erm cell loosens itself and migrates down 

 the tube. Its nucleus is set free by tlie disorganization of the 

 wall of the cell (if formed) and usually undergoes dixisiou. 

 thus makiug two or more s}")erins (figs. 321. 322). These 

 escape througli tlie ruptured wall of the end of the tube, 

 l)ass between the neck cells of the ovary and so fertilize the 



^'Kg (11" 393' H- 3^0- 



In angios|.)crms, in oixler that tlie sperm mav reach tlie 

 egg, the jxjllen tube must grow through (he tissues of the 

 stigma and style, or ])ass down the st\'lc canal to the interior 



