CONIFERS. 



455 



order to form the permanent embryo-sac. The nucleus of the embryo-sac is soon 

 absorbed, fresh nuclei being then formed in the parietal protoplasm, and free cell- 

 formation takes place round them. These cells soon unite laterally, grow in the 

 radial direction, and divide in such a manner that the embryo-sac is filled with 

 parenchymatous tissue. In those Coniferae in which the seeds take two years to 

 ripen, as Piniis sylvestris 2>x^A Juniper us communis, the endosperm formed in the first 

 summer is again absorbed in the spring, the protoplasm of the primary endosperm- 



FIG 324.— Taxus canadensis (after Hofmeister). A longitudinal section through the upper end of the endosperm 

 ee and the lower end of the pollen-tube/, cc the archegonia, ci their stigmatic cells, the left archegonium is fertilised, 

 X rudiment of the pro-embryo (June 5), (X300). B part of the endosperm with an archegonium, the pro-embryo of 

 which V is already further developed, /> the pollen-tube (June 10) (X200); C longitudinal section of a nucleus 

 (June 15), /fe /t nucleus, ee endosperm, p pollen-tube, vv two pro-embryos proceeding from two archegonia (X50). 



cells is set free by the deliquescence of their cell-walls, and forms by division a 

 number of new cells which, in May of the second year, again fill with parenchy- 

 matous tissue the embryo-sac now considerably increased in size. 



According to Strasburger's recent researches, the mother-cells of the 'corpuscula' 

 (archegonia' ) arise in the embryo-sac by free cell-formation in the same manner 

 as the first endosperm-cells ; but the septa by which the latter are transformed into 

 a multicellular tissue are not produced. The cells grow, on the other hand, more 

 vigorously, and divide near their apex where they touch the embryo- sac ; a large inner 



[See foot-note to p. 434.] 



