ANGIOSPERMS. 



;8i 



such as Allionia and Delphinium^ they are very large and well-developed. In the 

 Gramineae, Fischer has found that they divide and give rise to a considerable mass 

 of cells, a fact which Strasburger has ascertained with regard to Ornitkogalum, 

 though here it is exceptional. In some instances the two polar nuclei meet, not 

 in the centre, but towards the upper end of the embryo-sac; in this case the 

 upper nucleus is stationary, and the lower nucleus has to travel nearly the whole 

 length of the embryo-sac. This occurs, according to Fischer, in Elodea and in 

 many Gramineae, and apparently also in Allium fisiulosum. The coalescence of the 

 two polar nuclei usually takes place before fertilisation, but in Alisma and in Allium 

 fisiulosum it does not take place until the pollen-tube has reached the embryo-sac 

 or even until fertilisation has been actually effected. 



As regards the fate and the function of these various cells which are formed in 

 the embryo-sac, the oosphere is the one which undergoes fertilisation and developes 

 into the embryo, the others being transitory structures. The synergidae appear to 



Fig. j,^.~FuHkta cordata; A apex of the embryo-sac e, covered with a layer of cells belonging to the nucellus KK,x owe. 

 of the synergidae, 6 the ciosphere with its nucleus ; B, C oospore before, A £ after the first division ; I^ the spherical suspensor 

 with the two-celled rudimentary embryo (X Soo). 



cause the disintegration and in some cases at least the absorption of that part of the 

 wall of the embryo-sac with which they are in contact, and besides this, they have 

 a further function in the process of fertilisation to which reference is made below. 

 In. some cases {Crocus vernus, Torenia asialica, Sanlalum album) their pointed ends 

 become covered with a cap of a homogeneous substance which gives the reactions 

 of cellulose : by this means they replace that part of the wall of the embryo-sac 

 of which they have caused the absorption. After fertilisation the synergidae undergo 

 absorption. In many cases the antipodal cells soon undergo absorption, but in 

 some they persist, and may be seen at the base of the endosperm in the fertilised 

 ovule. 



We will now proceed to discuss these phenomena from a morphological point 

 of view. We have seen above that the cell which developes into the embryo-sac is 

 the equivalent of one of the mother-cells of the spores in the sporangium of a Vas- 

 cular Cryptogam, and to this we may add that it is equivalent to one of the mother- 

 cells of the pollen in the pollen-sac of the stamen. With this as the basis of their 



