80 
Our ignorance of the prothallium of the Ophioglosseze makes it 
impossible to determine positively their position, but as stated in 
a previous paper*, there is strong ground for regarding them as 
the most primitive of all the Filicinez. 
The greatest difficulty, it seems to me, in establishing a direct 
connection between the liverworts and ferns, is in the different 
character of the archegonium, and the spermatozoids. The form- 
er is very constant throughout all investigated liverworts and dif- 
fers in some important features from the same organ in the ferns. 
The spermatozoids too, are different in the two groups, being uni- 
formly bi-ciliate in the liverworts, and multi-ciliate in the ferns. 
This latter difference I regard as of great importance, and it is 
much to be hoped that a thorough investigation of this point in 
the liverworts will be made, to see whether there are forms that 
deviate from the ordinary biciliate type. ; 
It is by no means impossible that a careful examination of the 
hitherto unexplored regions of our country, especially the swamps 
of the Southern States, may bring to light forms which will help to 
solve the problem of the origin of the Pteridophytes, one of the. 
most important questions, certainly, in systematic botany. 
EXPLANATION OF FIGURES. 
In all the figures the apical cells are marked a. 
Fig. 1. Two very young prothallia of Osmunda Claytoniana x 150. Sp-Spore 
membrane. 
Fig. 2. Apex of an older prothallrum of the same. The limits of the younger seg- 
ments indicated by heavier lines. x 150. 
Fig. 3. Section of an older prothallium of an undetermined fern (Polypodiacez) 
a, at, a", the three apical cells x 300. Section parallel with the surface. 
Figs. 4,5. Two sections parallel to the surface, of prothallia of Osmunda cinna- 
momea with single four-sided apical cell. x 300. 
Fig. 6. Surface-view of a prothallium of the same species, showing the transition 
from the triangular to the four-sided apical cell. x 150, 
Figs. 7, 8. Vertical longitudinal section of the prothallium of Onoclea Struthiopteris, 
ar. Youngarchegonia. x 300, 
Fig. 9. Asimilar section of Osmunda cinnamomea; the younger segments are 
numbered. x 150. 
Fig. 10. Apex of a similar section, with the youngest segment still undivided. x 300. 
Fig. 11. A similar section of Dendroceros Breutelii (after Leitgeb). x 350. 
Figs. 1, 2, and 6 are from living specimens ; the others fixed with chromic-acid, 
and sectioned with the microtome. 
* Campbell, l. c. p. 3. 
