—ii7— 



plete and permanent, the edge being grown fast and the 

 sorus opening toward the apex. Numerous ferns pro- 

 tect their young sori by more or less completely sinking 

 them below the level of the frond's surface. According 

 to the extent of the immersion and the thickness of the 

 frond, the spots occupied by the sori may or may not be 

 prominent on the upper surface of the frond. When 

 they make moderately convex spots it strengthens the 

 frond mechanically, so that the fertile part of the frond 

 of Nephr odium Foxii retains its form for some time 

 after the sterile part has begun to wilt. In Mono gramma 

 and Vittaria the sori are in deep slits, the effect being as 

 in Asplenium pJiyllitidis, but the protection of the more 

 open slits is perfected by capitate paraphyses. In Poly- 

 podium incurvum, and more prominently in P. subauri- 

 culatum, P. nigrescens, P. schneideri and P. papillosum, 

 the sori are immersed for several times the thickness of 

 the frond, forming very prominent projections from the 

 upper surface. 



The structures that serve to prevent the dessication of 

 young sori serve also, without exception, to make their 

 exposure to liquid water impossible, and there are a con- 

 siderable number of ways in which they are adapted to 

 perform this latter function well. In other cases, struc- 

 tures at first clearly protective are done away with or 

 changed in such a way that as to make the mature spor- 

 angia as exposed as possible. Thus in a large part of 

 our Nephrodiums and in many of their relatives the in- 

 dusia partly or completely disappear as the sporangia ma- 

 ture. In Asplenium scandcns and without doubt in many 

 other species the indusia are motile, bending outward 

 when dry, but closely appressed when wet. This move- 

 ment deserves careful study both as to its commonness 

 and its mechanism. I have noticed it to exist, but in a 

 less pronounced manner, in Onychium. The indusia are 

 beset with hairs which I interpret as water-repellent 

 structures in various Kephrodiums, and are glandular 

 hairy or glandular ciliate in others. 



