14 



VASCULAR CRYPTOGAMS 



Flowering Plants this is the product of the action of the contents of the 

 pollen-grain on the protoplasmic embryonic or germinal vesicles ; in the 

 higher Flowerless Plants, of the action of the antherozoid on the oosphere, 

 or protoplasmic contents of the central cell of the archegone. The 

 naked masses of protoplasm known as the germinal vesicles (or perhaps 

 rather that one only which is ultimately fecundated) are therefore un- 

 questionably homologous with the naked mass of protoplasm known as the 

 oosphere. In Vascular Cryptogams the central cell which contains the 

 oosphere is a portion of an archegone which is borne on a prothallium 

 resulting from the germination of a spore or of a megaspore, as the case 

 may be. To understand the homologies with the higher Phanerogams 

 we must again have recourse to the intermediate Gymnosperms. In 



Fig. 4.— Female prothallium of Mar- 

 silca, with archegone a and oo- 

 sphere o. (After Hanstein.) 



Fig. ■\. — Fertilisation of Abies (Coniferae). /, 

 pollen-grains ; fs, pollen-tube ; e, embryo- 

 sac ; c, secondary- embrj-o-sac or corpusculum. 

 (X 60.) 



this class the female elements are not directly developed in the in- 

 terior of the embryo-sac, but within certain chambers produced within 

 the embryo-sac, the secondary embryo-sacs or ' corpuscula, the homo- 

 logues of the central cell of the archegone. In connection with them 

 there have been detected other structures comparable to the neck and 

 the canal-cells of the archegone. The object of the peculiar structure 

 of the archegone and the deliquescence of the canal-cells being to facili- 

 tate the passage of the motile antherozoids to the oosphere, these are 

 no longer wanted when impregnation is effected by means of a pollen- 

 tube. The archegone (except the central cell) is therefore reduced to 

 a rudimentary condition in Gymnosperms, and disappears altogether in 

 Angiosperms, where the embryonic vesicles are produced directly within 



