1922] 



PFEIFFER MONOGRAPH OF THE ISOETACEAE 151 



(Mo. Bot. Gard. Herb.); pools iy 2 mi. north of Limestone 

 Gap, 8 July, 1877, Butler (Mo. Bot. Gard. Herb, and U. S. 

 Nat. Herb.); pool by the railroad, Limestone Gap, 10 July, 

 1877, Butler (Mo. Bot. Gard. Herb, and U. S. Nat. Herb.). 

 Texas: wet pine-woods, Houston, 20 April, 1872, Hall 859 (Mo. 

 Bot. Gard. Herb., Gray Herb., and N. Y. Bot. Gard. Herb.) ; 

 Houston, May, 1872, Hall (Gray Herb.) ; swampy grounds, 

 Dallas, June, 1877, Reverchon 1177 (U. S. Nat. Herb.) ; wet 

 sands, Dallas, July, 1880, Reverchon 1177 (Mo. Bot. Gard. 

 Herb, and U. S. Nat. Herb.); mud, bogs, Buzzards' Spring 

 near Dallas, June, 1877, Reverchon 795 (Gray Herb.) ; Buz- 

 zards' Spring, 1879, Reverchon (Mo. Bot. Gard. Herb.) ; 

 dried pond, Sabine River Bottoms, near Mineola, Wood Co., 

 2 June, 1903, Reverchon 3551 (Mo. Bot. Gard. Herb.) ; shal- 

 low ponds, Pine's Island, Angelina Co., 5 May, 1903, Rever- 

 chon 3549 (Mo. Bot. Gard. Herb., Gray Herb., and U. S. Nat. 

 Herb.); Harrisburg, 9 May, 1876, Joor (Mo. Bot. Gard. 

 Herb.) ; rare in pond, Columbia, 17 October, 1900, Bush 1531 

 (Mo. Bot. Gard. Herb.); Hockley, 1891, Thurow 15 (U. S. 

 Nat. Herb.). 



Although the early material of 7. melanopoda appeared quite 

 uniform and therefore the species seemed distinctive, more re- 

 cent collections tend to add divergent forms. Engelmann early 

 described a variety pallida, which he based on "larger plants 

 lacking the black leaf bases of the type, with broader velum and 

 megaspores in the restricted range of 300-350 M, instead of the 

 250-400 M range given for the type." This was based on Texas 

 collections which upon examination show a wide difference in 

 spore sizes, running as high as 440 jj. These specimens do not 

 exceed northern forms in leaf number nor in leaf length. More- 

 over, it frequently happens that pale-based individuals are found 

 in any stand of 7. melanopoda, even though there be a prepon- 

 derance of dark-based forms. It seems proper, therefore, to con- 

 sider pallida as a form rather than as a variety of 7. melanopoda, 

 occurring singly or in stands. 



There is, moreover, intergrading between two species, in the 

 case of 7. melanopoda and 7. Butleri, so that some intermediate 

 forms are difficult to place accurately. As an illustration, the 

 examples originally described as 7. Butleri var. immaculata com- 

 bine in remarkable fashion the fine leaf habit of 7. Butleri with 



