120 



CORPUSCULUM : ARCHEGONIUM 



[CH. 



the protoplasm forms a plug. The four rosette-cells may 

 undergo a further horizontal division and become eight, 

 and other differences in detail may occur, but the above 

 typical example is not materially affected by these details. 



Fig. 28. Simple orthotropous ovule of the Yew. A, the mature ovule 

 seen from without; B, the same in section; C, the same ripened to a seed, 

 all slightly magnified. D, the ovule of stage B more highly magnified; a 

 commencement of arillus ; b scales of cone ; nc nucellus ; is integument ; 

 * micropyle ; edp endosperm filling the embryo-sac ; cjj archegonia. E, the 

 seed, at stage C, in section and more highly magnified ; a arillus ; e 

 embryo in the endosperm filling the embryo-sac. 



The large oval cell was long known as the Corpus- 

 culum a name given to it by Robert Brown, who dis- 

 covered it in 1834 but we shall find that this term, 

 now obsolete, does not help us to understand its 

 nature, and the best term to employ for the oval cell, 

 together with its rosette, &c., is Archegonium. 



This archegonium consists of two parts: the large 

 ovoid venter, sunk in the endosperm, and the rosette of 

 neck-cells, flush with the boundary between the endo- 

 sperm and the nucellus. The small plug-like cell which 

 protrudes between the neck-cells is known as the ventral 

 canal-cell, and it opens the neck and subsequently affords 

 a passage through it by dissolving. The large nucleated 



