XII] 



PROTECTION OF THE SORUS 



239 



example of this is seen in the world-wide Acrostic/mm aureum. It appears 

 as though the adult sporangia of such plants had become less susceptible 

 to exposure than their predecessors. Nevertheless the young sporangia are 

 often well protected. The soral area is frequently very closely packed, as 

 in Leptocliihis tricuspis, so that the younger and shorter sporangia are pro- 

 tected by the older and higher, while these as they grow up expose their 



Fig. 237. Vertical sections through the margins of fertile pinna of various species of Blechnum, 

 showing how the "flange" has arisen as a new formation. A. Blechimni discolor, there is no 

 flange. (X125.) ^. Z". /e««a-wrtrma, flange slightly indicated. ( x 1-25.) C. i5. /raj«7, flange 

 of considerable size bearing a stoma. (X50. ) D. B. L' Hcrmim'eri, flange still minute. (X50.) 

 E, F. B. procera, the flange has distinct marginal segmentation; the "indusium" which is the 

 real phyletic margin arises superficially and is delayed. ( x 125.) G. B. brasiliense, this state is 

 still more pronounced than in B. procera. { x 125.) H. B. occide7itale, shows the early segmenta- 

 tion of the flange, while the receptacle and "indusium" would arise later at point of star (*). 



heads freely for dehiscence. But besides this such sori are often provided 

 with numerous hairs, which branch, and are sometimes peltate, sometimes 

 glandular. These means of protection are shared by many Polypodiaceous 

 Ferns that have definite sori. Such protections by branched hairs are seen 

 in Metaxya, Niphobolus, and Platycerium : by glandular hairs in Vittaria, 

 and Acrostichuin mireum: by scales in Poly podium litieare, verrucoswn, and 

 piloselloides, and in Drymoglossum. Occasionally hairs are borne upon the 



