The Extent of the Annulus, and the Function of the different Parts 
of the Sporangium of Ferns in the Dispersion of Spores.* 
By GEo. F. ATKINSON, 
A study of the sporangia of the different families of ferns made 
to determine the character of the so-called “complete annulus” 
makes it necesary to place some restrictions upon the use of that 
term as applied to the part of the annulus concerned primarily in 
the dispersion of the spores. 
In the Polypodiacee the annulus is said to be “incom- 
plete.” It extends from the distal end of the stalk over the 
dorsum and vertex of the sporangium to the anterior upper 
angle. The lip cells in the front possess thickened and ligni- 
fied walls, and between them the line of cleavage occurs 
at the moment of dehiscence. Between the upper lip cell 
and the anterior end of the annulus are two or three cells 
with walls exactly like those of the lateral walls of the 
Sporangium. Similar cells also exist between the lower lip cell 
and the distal end of the stalk at the lower angle of the sporan- 
gium. These cells serve as connectives between the lip cells and 
the anterior end of the annulus on the one hand and the stalk on 
the other. At the moment of dehiscence they serve as a pull 
upon the lip cells as the annulus is everting. The lip cells being 
- Situated at the middle of the front divide the sporangium in halves 
and the line of cleavage started continues straight across the lat- 
eral walls of the sporangium. The connectives serve also an- 
other very important function. They are passive like the lateral 
walls and thus the halves of the sporangium remain intact while 
the annulus is being everted and preparing to spring. By this 
means the spores are held in place until the annulus springs when 
they are hurled violently away. 
In the Cyatheacez, Gleicheniacez, and shy dienepb yuancee the 
annulus is said to be “complete,” 2. ¢., it extends entirely around 
the sporangium. 
* The substance of this paper was s presented before the botanical section ok the 
A.A. A, S, at the Madison Meeting. 
