282 



PLANT LIFE. 



vided to receive it. The wall cell remains undivided and 

 grows to form an unseptate filament, called the "pollen 

 tube" (figs. 317, 318, 319, 321, 322, 323). In gymno- 



Fig. 314. 



Fig. 314. — Vertical median section of the mature spermary of a fern [Adiantutn 

 capillvs-veneris). /. adjacent cells of gametophyte (figs. 74, 77) j , ( , spermary, show- 

 ing wall composed of three cells, the two lower (above and below letter a) being ring- 

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

 nally single, has divided into a number, the sperm mother cells, which at this stage are 

 loosened and contain each a fully developed coiled sperm. Magnified 550 diam. — 

 After Sachs. 



Fig. 315. — A vertical median section of the gametophyte of Selaginella stolonifera. 

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

 314) ; w, the cells forming the wall of tile spermary; ,f, the mother cells of the 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 

 w allows the sperms to escape. Magnified 640 diam. — After Strasburger. 



Fig. 316.— Diagram of the gametophyte of the larch (Larijc Europaa), formed in the 

 microspore. /, the vegetative cell ; st , two stalk cells of the spermary; s, cell whose 

 nucleus subsequently divides to form two sperms (the walls of the mother cells not 

 forming) ; w, the wall of the spermary which remains undivided. Compare fig. 315. 



sperms this penetrates the megasporangium (ovule body) and 

 reaches the female gametophyte on whose surface are formed 

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

 development the sperm cell loosens itself and migrates down 

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

 wall of the cell (if formed) and usually undergoes division, 

 thus making two or more sperms (figs. 321, 322). These 

 escape through the ruptured wall of the end of the tube, 

 pass between the neck cells of the ovary and so fertilize the 



egg (11 39 3> fi g- 32i)- 



In angiosperms, in order that the sperm may reach the 

 egg, the pollen tube must grow through the tissues of the 

 stigma and style, or pass down the style canal to the interior 



