578 



FILICALES 



one hand, and on the other to the Osmundaceae and certain of the 

 early fossils. The general construction of the Hymenophyllaceous sorus 

 is well known. Many satisfactory drawings are given by Presl, and 

 other descriptive writers, which show how the 

 sporangia with their oblique annulus are disposed 

 with regularity of orientation upon the elongated 

 receptacle, so that they overlap one another like 

 the shields of a Roman testudo. The orientation 

 for each single sporangium corresponds essentially 

 with that seen in Gleichenia or Loxsoma. This is 

 well shown for Trichomanes in the drawing of 

 Goebel (Fig. 324). The sporangia are produced in 

 basipetal succession upon the more or less elongated 

 receptacle. This fact is demonstrated in Fig. 324^/5-, 

 which represents the young sorus of Hymenophyllum 

 Wilsoni already bearing the young sporangia (s) near 

 the apex of the receptacle, while below there are clear 

 indications of the active intercalary growth. The 

 extent of the intercalary growth of the receptacle is 

 greater in Trichomanes than in Hymenophyllum, 

 and the genera were by early writers distinguished 

 on this ground, those with the receptacle exserted 

 being ranked with the former, while those with it 

 included fell into Hymenophyllum. Though this 

 generic distinction will not hold accurately, still the 

 general statement is correct that intercalary growth 

 of the receptacle, and basipetal succession of the 

 sporangia are longer continued in Trichomanes', it 

 is the extreme example of this mode of development 

 of the sorus among Ferns, but none the less is it 

 similar in kind to that described for other Gradatae. 

 The sporangia in the Hymenophyllaceae differ 

 greatly in size, between a large, almost spherical 

 type, such as that of Hymenophyllum dilatatum (Fig. 

 325, Nos. 95, 96, 97, 98), and small compressed 

 bodies such as are formed in many species of 

 Trichomanes (Fig. 325, Nos. 99, 100, 101, 102); 

 it will be shown that with this goes a very wide 

 difference in the output of spores. The large 

 sporangia of Hym. dilatatum are produced in relatively small numbers 

 upon the short, but rather broad, receptacle ; in size and form they are 

 comparable to those of Gleichenia circinata (compare Fig. 325, No. 95, 

 with Fig. 310 i of Gl. circinata\ while the annulus shows a similar degree 

 of obliqueness. Externally there is close similarity, excepting in the dehis- 

 cence, which is lateral in Hymenophyllum, a position which we shall see 





FIG. 324. 



Trichomanes tenerum. 

 Sorus in surface-view ; the 

 placenta bearing radially 

 distributed sporangia issues 

 from the two-lobed beaker- 

 like indusium. The annulus 

 is visible on the several 

 sporangia. Magnified. (After 

 Goebel.) 



