CHAPTER III. 
REPRODUCTIVE ORGANS OF FERNS. 
The Sonr— Their form and position—Dorsiferous and Marginal-fruited Ferns.—The 
RECEPTACLE—its systematic value—its position. —The SPORE-CASES—Annulate 
and Exannulate, or Ringed and Ringless Ferns— Vertical and Oblique rings— 
Rudimentary ring—Indusium—Involucre— Indusiate and Non-indusiate Ferns, 
一 The Sporrs—Their germination— Prothallus— Antheridia—Pistillidia or 
Archegonia. 

Tue Reproductive Organs of Ferns consist of spores, enclosed 
in spore-cases, sometimes called sporangia, thecw, or capsules, these 
spore-cases being collected into groups of varied form, called sori 
(sing. sorus). 
The Sori consist of the spore-cases, collected together into groups 
of various outline, usually forming distinct spots, round or oblong, or 
lines more or less extended, and occupying different positions with 
respect to the venation. They are generally situated on the plane 
of the frond, or slightly clevated, and are then called superficial; 
but sometimes they are seated in a groove or channel, and they are 
then said to be immersed. The principal forms assumed by the 
sorus are :—the punctiform, i. e., forming round dot-like clusters ; 
the oblong or linear, i.e., forming lines, short or long, which lines 
may be either marginal, costal, or oblique, and either simple or 
united like net-work, following the veins; the amorphous, 12075 
forming large shapeless patches; and the universal, i.e., covering 
the whole surface. 
In the annulate Ferns, which comprise all the Polypodiacee, the 
sori are usually borne on the under surface, or, what is usually 
called the back of the frond. The sori are then said to be dorsal, 

