4GG EXPLANATION OF THE FIGURES. 



PLATE XXVIII. 



Figs. 1 6. Pteris aquilina. 



FIG - 



1. Archegonium, with the adjoining cells of the prothallium, in longitudinal 



section. The embryo consists of four cells lying in the plane of the sec- 

 tion. X 300. 



2. Longitudinal section of the fore part of the cushion of a prothallium, which, 



besides the impregnated archegonium laid bare by the section, and 

 whose central cell is not quite filled by the rudimentary embryo, bore a 

 second impregnated archegonium with a far more developed embryo. 

 Above the cushion of cellular tissue there is seen a portion of the mem- 

 branous wing of the prothallium, which has been cut by the section, x 

 150. 



3. An unimpregnated archegonium, and one which has been some time im- 



pregnated, in a longitudinal section of one and the same prothallium. 

 X 300. 

 3*. The cellular net of the embryo of the latter figure. The lines which 

 answer to the boundaries of the cells of the older generation are much 

 thickened. The group of cells ac is the rudiment of the principal bud, 

 and of the first frond ; the group a d is the rudiment of the root. 



4. A similar preparation from a more developed prothallium. The cells of 



the first degree of the root are here very visible. X 300. 



5. Longitudinal section through the cushion of cellular tissue of a prothallium. 



The section has passed through an archegonium with a far more deve- 

 loped embryo. X 300. 



Tigs. 7 8. Pteris serrulata. 



7. Optical transverse section of the central cell of an archegonium just im- 

 pregnated. The germinal vesicle contains two nuclei. X 300. 



S. Longitudinal section of a prothallium, with an embryo in the^state of 

 development of that of Pteris aquilina, as shown in fig. 5. X 35. 



PLATE XXIX. 



PTERIS AQUILINA. 



Longitudinal section of a young plant which has recently broken through 

 the archegonium. A portion of the prothallium to which it is 

 attached is figured. X 150. 



Imaginary outline of a more developed germ-plant B the primary axis, 

 a the first, r> the second frond ; between the two the position of the 

 apical cell is indicated ; c the first, E the second, r the third adventi- 

 tious root. 



The fore-edge of the first frond of a germ-plant in the same state of deve- 

 lopment, seen from the fore-surface, x 100. 



