38 OUR NATIVE FERNS AND THEIR ALLIES. 



In this way valuable additions to science may be contributed 

 by those whose labor misdirected might be wasted. 



1 OO. Fructification. The sporangia of the quillworts, 

 like those of the club-mosses, are sessile in the base of the 

 leaves. The leaf base, sometimes called the sheath, is some- 

 what triangular from the broad insertion, convex behind and 

 concave in front, where there is a 



/ '1A I llti large depression known as \hefovea> 



which contains the sporangium. 

 The margin of the fovea rises in the 

 form of a delicate membrane called 

 the velum, which in many species 

 lies above the sporangium and en- 

 closes it. The sporangia of the outer 

 FIGS. 28, 20. Two kinds of , , i_- i 



sporangia In /. lacustris L., en- leaves contain large spherical ma- 

 larged. (After Sprague.) crospores ; those of the inner con- 



tain numerous oblong, triangular microspores. The size and 

 marking of the spores form important characters in distin- 

 guishing species. 



1 O 1 . Germination. The microspore after remaining dor- 

 mant through the winter forms a few-celled structure which 

 produces the antherozoids, which are long and slender, and 

 provided with a tuft of cilia at each end. The macrospore 

 produces a prothallium much as in Seluginella (97) ; from this 

 the germ of the mature plant arises after fertilization by the 

 antherozoids. 



LITERATURE. 



BAKER (J. G.). Fern Allies, pp. 123-134 (1887). 



BRAUN (Alexander). On the North American Species of 

 Isoetes and Marsilea. Communicated by Dr. G. Engelmann. 

 In Sillimaris Journal, Second Series, in, 52-56 (1847). 



ENGELMANN (George). Isoetes of Northern United States. 

 In Gray's Manual, Fifth Edition (1868). 



The Species of Isoetes of the Indian Territory. In Bo- 

 tanical Gazette, ill, i, 2 (Jan. 1878). 



The genus Isoetes in North America. In Trans. St. 



Louts Acad. Set., IV, 358-390 (1882). A valuable monograph of 

 this most difficult genus of the fern allies. 

 See also notes in Botanical Gazette, vi, 228. 



