—ii3— 



tropism of the stem, determining" whether it shall be 

 prostrate or erect, nor its symmetry, radial or bilateral, 

 seems to be a very deep-seated or firmly fixed character, 

 for both change in many instances within universally 

 recognized generic or subgeneric limits. 



Fleshy rhizomes serving as water reservoirs are found 

 in Dfynaria and its relatives, most notably in Poly podium 

 heracleum and less developed in Photinopteris and Poly- 

 podium affinc. All rhizomes are protected against loss of 

 water at the apex and many throughout their length by 

 scales which vary in form, size and texture. Exceed- 

 ingly harsh palae are found on Dipteris and Demist cedtia 

 Williamsi, two ferns with notably stout rhizomes. It is 

 very probable that these are protective against animals 

 such as deer and hogs, which are very numerous, but 

 which never, so far as I have observed, touch these 

 species. Similar scales protect the fleshy crowns of va- 

 rious Cyatheaceae. The muricate stems of Stenochlcena 

 and muricate stipes of Dennstccdtia erythrorachis and 

 other species probably have the same function. Dead 

 bases of stipes must provide other rhizomes with an 

 unpalatable mantle, but most fern stems are too hard to 

 need protection of this kind. Many steins contain chloro- 

 phyll when exposed to light. It is regularly present in 

 those of Poly podium accedens, P. dolichopterum, P. com- 

 mutatum and P. Schneideri. 



The correlation between length of rhizome and length 

 of stipe has just been mentioned. A similar correlation 

 exists between length of one or the other of these and 

 the development of the lowest pinnae. Deltoid fronds — 

 that is, fronds with elongate lowest pinnae — would seri- 

 ously interfere with each other's light if they were not 

 borne on wide-creeping rhizomes or on very long ascend- 

 ing stipes or on comparatively short but more horizontal 

 stipes. Fronds with short stipes, unless these are very 

 remote, usually have the pinnae reduced toward the base. 

 "Under the same conditions, entire fronds are narrowed 



