Notes. 
323 
the mixed character the drain may be spread over an equally long time, 
while, as the elongated receptacle disappears, the surface from which 
nourishment can be derived is enlarged, and the distance through which 
it has to be transferred is shortened. Thus it appears biologically 
reasonable that the succession should be as suggested. 
It is shown how the various types of dehiscence and the action of 
the annulus stand in close relation to the orientation of the sporangia, 
and to their arrangement in the sorus. Thus the position of the 
annulus, which has played so important a part in classification, has 
been placed upon a footing of adaptation. 
Estimates of numerical output of spores per sporangium have been 
made with a view to illustrating the relation of the Eusporangiate and 
Leptosporangiate Ferns in this respect. The estimated output in the 
Marattiaceae has been shown to be high 1 ; that of the Polypodiaceae 
is sixty-four or less. The result of numerous countings is to show 
that, of all Leptosporangiate Ferns, Gleichenia approaches most nearly 
to the Marattiaceae ( Gl . flabellata may produce over 800 per sporan- 
gium) ; Osmunda may have over 500, and Lygodium 25 6. The most 
interesting results were derived from the Hymenophyllaceae, in which 
Hym . tunbridgense may have over 400, while species of Trichomanes 
may produce as few as thirty-two per sporangium. These results, 
when taken with those derived from the filmy Todeas, make it seem 
probable that the filmy habit is a condition leading to reduction of 
output per sporangium, and indicate that the Hymenophyllaceae are 
a derivative series of reduction. 
A most important commentary upon the classification proposed is 
derived from comparison of the antheridia, which Heim 2 found to be 
the most dependable part of the gametophyte for comparative purposes. 
He recognizes two types according to their dehiscence : the one type 
includes, with the exception of two genera of Schizaeaceae, our Sim- 
plices and Gradatae, while the other includes the Mixtae. I can only 
regard this correspondence of parts, so aloof from one another as the 
antheridium and the sporangium, as establishing the relations of 
the Simplices and Gradatae upon a firmer footing ; the facts also give 
substantial support to the distinction of the Gradatae and Mixtae. 
The effect of the observations and comparisons in this memoir is 
rather confirmatory of the current classifications than disturbing. The 
divisions suggested would supersede those of Eusporangiatae and 
1 Studies, No. 3, p. 60. 2 Flora, 1896, p. 355, & c. 
