ANGIOSPERMS. 



391 



The pollen-tube having passed through the micropyle either encounters the 

 exposed apex of the embryo-sac, or, as in Watsonia and Santalum, the projecting 

 synergidae ; but very frequently a portion of the tissue of the apex of the nuccllus 

 is still in the way, and the tube must penetrate it to reach the embryo-sac. The 

 wall of the latter is often weak and is sometimes indented by the advancing end 

 of the tube, or even, as in Canna, pierced by it. 



I 



FIG. 321. Development of the embryo-sac, fertilisation and embryogeny in an orchidaceous plant, a combination 

 of figures of Gymnndenia Conopsea and Orchis fallens. I rudiment of the mother-cell of the embryo-sac, and of the 

 inner integument. // division of this mother-cell of the embryo-sac into three sister-cells, the lowest of the three being the 

 rudimentary embryo-sac. /// displacement of the two upper sister-cells by the growing embryo-sac ; two nuclei in the 

 sac. //'doubling of the two nuclei. J' further division of these nuclei. VI the egg-apparatus in the anterior extremity 

 of the embryo-sac consisting of the two synergidae and the oosphere beneath them ; the three antipodal cells are in the 

 posterior end of the embryo-sac, and there are two free nuclei in its cavity, yjl the mature ovule before fertilisation 

 the two free nuclei of the embryo-sac have coalesced and formed a secondary nucleus which still contains two nucleoli 



VIII fertilisation by means of one of the synergidae (the one to the right) which appears to be changed into a homo 

 geneous highly refractive protoplasmic body; there are two nuclei, the sperm-nucleus and the nucleus of the oosphere 



IX pro-embryo consisting of two cells. A~ further development of the pro-embryo. The letters em denote the mother 

 cell of the embryo-sac (archesporium), e the embryo-sac, pek the primary nucleus of the embryo-sac, sek the secondary 

 nucleus of the same, s the synergidae, o the oosphere, i r the antipodal cells, / the pollen-tube, k the pro-embryo in process 

 of differentiation, ii the inner, ai the outer integument,./ the funiculus, It an intercellular space. From drawings by 

 Prof. Strasburger. "// is magn. about 200 times, the rest about 300 times. 



The contact of the tube with the apex of the embryo-sac or with the filiform 

 apparatus of the oosphere is sufficient for the transference of the fertilising substance ; 



