— n8 — 



It has already been stated that paraphyses are in gen- 

 eral water-repellent structures, in adaptation to which 

 function they are provided with oily heads. The para- 

 physes are in part a substitute for indusia and often 

 occur on ferns such as Acrosticheae, which could not have 

 indusia, but they are not rarely present in indusiate sori. 

 They are notably developed on Lomagramma and Acros- 

 tichum, the brown color of the surface of the latter being 

 due to them, while the sporangia are green. The 

 branched form, like the oiliness, is evidence that they 

 are specialized for protection against water rather than 

 against dessication. Hairs on the end of the sporangia 

 have the same effect. They are found in a number of 

 species of Nephrodium, such as N. setigerum (gland- 

 ular) and N. diversilobum. These hairs on the ends of 

 the sporangia make the whole sorus incapable of being 

 wet. Spores of ferns in general are not readily wet, be- 

 cause of their waxy and often rough or reticulate sur- 

 faces. Their resistance to wetting not merely facilitates 

 their dispersal but insures them against germination 

 under too temporarily favorable circumstances. 



Very numerous ferns provide in a variety of ways 

 that the dryness necessary for the dispersal of the spores 

 shall involve the least possible dessication to the vegeta- 

 tive frond. One very simple means to this end is the 

 location of the sori on the margin, or even on teeth. 

 The marginal or apical position of the sori has been as- 

 sumed independently by the plants in many different 

 groups of ferns. As the primary purpose of this posi- 

 tion of the sori is to insure the dryness of the sporangia 

 and spores, it is characteristic of the plants growing in 

 the most moisture-laden atmosphere, as in the rain- and 

 mossy-forests. The tooth position is obviously drier than 

 the merely marginal. The Lindsayas growing in the 

 moistest places are deeply cut — even finely dissected in L. 

 Blumcana of the mossy forest of Luzon. Yapp suggests 

 that the peculiarly placed sori of Lccaiwptcris will let 

 the spores escape only when there is wind enough to be 



