REPRODUCTIVE CELLS. 



133 



several peculiar flask-shaped structures, the archegonia,* and the 

 early formation of an archegonium (see Fig. 102) is as follows: — 

 One of the apical cells of the prothallium divides into two, 

 and the lower of these divides again. The lowest or larger 

 cell is the archegonium proper, and contains an oosphere com- 

 posed of cytoplasm and large nucleus. The upper cells, by 

 further divisions at right angles to the former ones, gi^-e rise 

 to cells which separate in the centre and leave a space, the 

 canal of the archegonium (see Figs. 102 and 103). A few cells 

 are soon cut off from the upper part of the oosphere, the lowest 



Fig. 101. — A Longitudinal Section' or the FituiT-scAiiE (Maceosporo- 

 phyll) and Beact of Pinus, to show relations of the embryo-aao 

 and nucellus. — sk, Fruit-scale; hr, bract; 7il\ nucellus; mp, micro- 

 pyle; es, embryo-sac (prothallium or "endosperm" already formed) ; 

 svi, the "samara" or wing of the ovule; xy^, p\, xy^, ph^, the xylem 

 and phloem of the scale and bract respectively : note that the relative 

 positions of these are reversed in the fruit-scale, the phloem being 

 uppermost. 



*The " corpuscula " of earlier writers. Each archegonium was formerly 

 erroneously looked upon as a separate embryo-sac, but, strictly speaking, 

 the corpuscula = oospheres. 



