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, wliere there is a 

 large depression known as \}a&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 

 lies above the sporangium and en- 

 closes it. The sporangia of the outer 

 Figs. 28, 20. — Two kinds of , ^ . , 1 • „i .„„ 



sporangia in /. lacustris L., en- leaves contam 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. 



101. Germination. — The microspore after ren.aining 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 Schxi^^inclla (97J ; 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 Silliman's Journal, Second Series, III, 52-56 (1847). 



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

 Isoetes. In Annals of Botany, V, 231-25S, pi. xv-xvii (1891). 



Engelmann (George). Isoetes of Northern United States. 

 In Grays Manual, Fifth Edition (1868). 



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



tanieal Gazette, III, i, 2 (Jan. 1878). 



The genus Isoetes in North America, 



In Trans. St, 



