SECT. VIII. 



SPORANGIA. 



343 



the stoma, where the horizontal bursting takes place. 

 This form is seen in fig. 56, a, b. In other groups 

 it is, though vertical, 

 somewhat oblique, as in 

 fig. 56 c. Sometimes, 

 though more rarely, it 

 is transverse and com- 

 plete ; in which case the 

 rupture is vertical, as in 

 fig. 56 d. In a few cases 

 it is apical, fig. 56 e, and 

 in a few others it is ob- 

 solete, fig. 56 /. These 

 are the true Ferns. In 

 one or two small groups, 

 sometimes called Pseu- 

 do-Ferns, the ring is al- lg ' - 6 

 together wanting. 



The systematic arrangement of the Ferns is chiefly 

 founded on peculiarities of the sori and sporangia, 

 characters which are quite intelligible by the aid of 

 a good magnifying lens, these spore-cases being very- 

 pretty opaque objects under the microscope. Thus some 

 of the primary divisions are founded on the presence 

 or absence of the ring or annulus on the spore-case. 

 Another series of divisions are founded mainly on the 

 nature of the ring in those cases when it is present ; and, 

 for the rest, the form and position of the sori come in 

 as discriminating characters. In this way the main 

 groups are marked out, but, in the case of the genera, 

 still further recourse is had to the sori and its covering, 

 and by some modern authors supplementary characters 

 derived from the venation are brought into use. The fol- 

 lowing is the arrangement adopted by Mr. Moore, 7 and 



7 'Index Filicum,' by Thomas Moore, F.L.S. 



Sporangia of Polypodiaceous Ferns : 

 a, b, Polypodiaceae ; c, Cyatheineae; d. Glei- 

 chenineae ; e, Schizasineae ; /, Osmundineae. 



