THE HIGHER CRYPTOGAMIA. 193 



favorable to the production of sexual organs as well as of 

 roots. 



In Ceratopteris thalictroides, the antheridia of which 

 are abnormal in position and structure, prothallia occur 

 having numerous cushion-like masses of tissue in which 

 archegonia are produced, each one of such cushions being 

 situated behind one of the numerous indentations of the 

 edge of the prothallium. 



At an early period, even before the complete formation 

 of the neck, a secondary free nucleus appears in the 

 upper part of the central cell of the archegonium. The 

 large primary nucleus of the central cell is still present. 

 The secondary nucleus is soon seen to be surrounded by 

 a free spherical cell, in close proximity with the internal 

 surface of the apex of the central cell (PI. XXV, figs. 

 5 9). This is the germinal vesicle. When it first 

 appears its diameter is only about one sixth of that of the 

 central cell, but, even before the bursting of the apex of the 

 archegonium, it grows, to almost one half the size of its 

 mother-cell. For some time after its appearance the 

 primary nucleus of the central cell remains unchanged 

 (PL XXV, figs. 3, 5, 8) : at a later period it disappears ; 

 this takes place before the opening of the apex of the neck 

 of the archegonium (PI. XXV, figs. 4, 7, 11). 



The cells of the inner tissue of the prothallium which 

 arc adjacent to the central cell of the archegonium, di- 

 vide repeatedly by septa at right angles to the bounding 

 surfaces, and by this means are converted into a kind of 

 epithelial layer, consisting of narrow cells containing a 

 quantity of finely granular protoplasm (PL XXV, figs. 3, 

 5, 11). The period of the commencement, and the in- 

 tensity of this multiplication, are very different in indivi- 

 dual instances. (Compare PL XXV, fig. 3, with PL XXV, 



figs. 4, 7.) . 



During the formation of the germinal vesicle a wide 

 canal leading to the embryo-sac is formed in the longi- 

 tudinal axis of the neck of the archegonium. The apex 

 of the neck of the archegonium remains firmly closed 

 during the development of this canal. In most cases 

 during the progress of this development, the cells of the 



