ENGELMANN — THE GENUS ISOETES IN N. AMERICA. 386 



a tributary of Coosa river, Floyd Co., in slow-flowing water ablut a foot 

 deep- A. TV, Chapman, 



The trunk of this species is larger than I have seen it in any other, and 

 more variable in form; sometimes it is quite flat and over one inch wide, 

 especially in van valida, or it is thick; and I have seen it even twice as 

 high as it was wide, 4J lines wide in the largest transverse diameter and 7 

 lines high ; this, however, is a w^ry unusual form. The plant is submerged 

 in spring with the leaves partly floating; later, when the water recedes, 

 the older leaves are spread out on the mud, but the later growth becomes 

 erect; var. gracilis is often more or less submerged, and its weakly devel- 

 opement is probably owing to this circumstance, while var. valida is the 

 stoutest form we have, and one of the stoutest in the whole genus, perhaps 

 only /. Malinveriajia of the rice fields of Lombardy surpassing it. Avery 

 small form, only 5 inches high, has been collected in a springy place on a 

 rocky hillside near Wilmington, Del., by A. Commons, otherwise not dis- 

 tinct. The Georgia variety, characterized by its larger spores, ought to be 

 further studied. In my Missouri specimens I find, among many of the ordi- 

 nary type with white sporangium, a few where this organ is uniformly 

 brown, not spotted. The dissepiments of the leaves consist, the median 

 of 3 to 4 and the transverse one of 2 to 3 layers of cells- The well marked 

 reticulation of the macrospores is formed of very thin fragile lamince, not 

 of thick ridges as in some other species. 



10. L HowELLii, Engelm. n. sp. Middle sized, leaves (10 to 25) bright 

 green (5 to 8 inches long) with thick dissepiments; sporangium oval (i^ 

 to 2i lines long): unspotted, i to .} covered by the velum ; subulate ligula 

 as long as sporangium; macrospores 0.43 to 0.4S mm. in diam., rough, 

 with prominent rounded single or sometimes confluent tubercles. 



On border of ponds at the Dalles of the Columbia, Oregon, J, d- T. J. 

 Howell, 18S0, not quite mature in June. - I insert this species which has 

 just been communicated to me through the kindness of Mn G. E. Daven- 

 port, while the manuscript is in the hands of the printer; this must excuse 

 some discrepancies in the foregoing pages, where no reference could be 

 made to it. The new species is distinguished from the similar /. Bolan- 

 deri by the longer leaves, larger more prominently marked macrospores, 

 and especially by the distinct peripheral bast-bundles, which place it near 

 the foregoing one, by the thick dissepiment consisting of 4 to 6 layers of 

 cells, and by the unusually narrow and long ligula; the tubercles of the 

 spores are quite prominent, as high as they are wide, rounded at top; 

 micro^^pores light brown, smooth.- Among the specimens ot this species, 

 and probablv collected with it, I find a single one similar in the structure of 

 the leaf, but' without a trace of a velum, the sporangium bemg entirely 

 naked and only attached by the median line to the leaf base ; it is unfortu- 

 nately immature, and can only be indicated as a probably new species, 

 / nuda This would not be the first instance of two species growmg 

 together In the same pond or lake ; in Mystic Pond we find /. Tuckerjnani 



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