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 

 large depression known as the fovea, 

 which contains the sporangium. 

 The margin of the fovea rises in the 

 form of a delicate membrane called 

 the velum, which in many species 

 ■^B^Mf I V ■ ■*a2»'->v I'^s above the sporangium and en- 

 -—'~—^ — ^ closes it. The sporangia of the outer 



Figs. 38, ag. — ^Two kinds of , ^ . , i_ • i 



sporangia in /. lacusiris L., en- leaves contam large spherical raa- 

 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. 



101. 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 Selaginella (97) ; from this 

 the germ of the mature plant arises after fertihzation 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, ill, 52-56 (1847). 



Campbell (D. H.). Contributions to the life-history of 

 Isoetes. In Annals of Botany, v, 231-258, pi. xv-xvii (1891). 



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. 



