EXPLANATION OF THE FIGURES. 473 



PLATE XXXVIII. 



EQTJISETUM ARVENSE. 

 FIG. 



1. Longitudinal section of an archegonium shortly before the opening of the 



apex, x 300. 



2. The same immediately after the opening, x 300. 



3. Perspective view of an archegonium lately opened, shown by means of 



two parallel longitudinal sections of the prothallium, x 300. 



4. Longitudinal section of an archegonium just impregnated, x 300. 



5. 7 — 10. Detached embryos in different stages of development, seen in lon- 



gitudinal section, x 200. 



6. Longitudinal section of an impregnated archegonium, with the embryo in 



the central cell, x 300. 

 11. Accidental transverse section of a rudimentary embryo, x 200. 



PLATE XXXIX. 



1, 2. Longitudinal sections of impregnated archegonia, with embryos; fig, 1, 

 before the falling off of the cells of the mouth ; fig. 2, after the same, 

 X 200. 



3. Longitudinal section of a lobe of a prothallium, with two impregnated 



archegonia, x 200. 



4, 5. Embryos more advanced, seen in the front, so that both the primary and 



the secondary axes are in the line of sight, x 200. 

 6. Longitudinal section of the lower part of a germ-plant, at about the stage 

 of development of fig. 3 in the next plate, X 100. 



PLATE XL. 



1. Lobe of a highly developed prothallium cut through longitudinally. Be- 



sides abortive archegonia, the section has exposed an impregnated one 

 with a considerably developed embryo. X 100. 



2. Embryo just breaking through the prothallium, shown in longitudinal 



section. 



3. Portion of a prothallium with a germ-plant, whose root and first leafy shoot 



have recently emerged from the prothallium, X 10. 



PLATE XLI. 



Eigs. 1 — 4. Ophioglossum vulgatum. 



] . Longitudinal section of a stem at the beginning of December. Above, on 

 the left, is a rudimentary pair of fronds (about \ inch long), destined for 

 development in I he following spring. The section is exactly through 

 the median line of the protuberance of cellular tissue, which is situated 

 somewhat laterally in front of the latter frond, and which encloses the 

 younger fronds, x 20. 



