1922] 



PFEIFFER — MONOGRAPH OF THE ISOETACEAE 151 



(Mo. Bot. Gard. Herb.); pools V/% 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 



Dallas 



795 (Gray Herb 



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 /. 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 p, instead of the 

 250-400 n 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 _i. 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 /. 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 /. melanopoda, 

 occurring singly or in stands. 



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

 case of /. melanovoda and /. Butleri so that some intermediate 



forms are difficult 



As an illustration, th 



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

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



