WATER FERNS 259 



Maidenhair of the North {Adiantum pedatum), and of 

 the South {A. capillus-ve?ieris) , the common Brake 

 {Pteridium aquilinum) the Spleenworts (Asplenium) of 

 many species, the Shield-ferns (Aspidium), also of many 

 species, the curious little Walking- fern {Camptosorus 

 rhizophyllus), the Bladder-fern (Filix fragilis) and the 

 large Ostrich-fern {Onoclea struthiopteris) . 



462. Some of the Modern Ferns have become aquatic 

 and hence are known as Water Ferns 

 (Order Marsiliales) in which two kinds of 

 spores ("heterospores") are produced, mic- 

 rospores and megaspores, which in time give 

 rise respectively to antheridial, and arch- 

 egonial gametophytes. The Marsilias are 

 rooted plants, with floating, 4-parted leaves, 

 while the Salvinias are small, floating, nearly rootless 

 plants, with simple leaves. 



Laboratory Studies, (a) Collect several different kinds of 

 common ferns, including the underground portions as well as 

 the leaves. Study the vascular bundles, stone tissue, and 

 fibrous tissue in the underground stem. 



(6) Examine the disposition of the small vascular bundles in 

 the leaves, whether free or reticulated. Peel off a bit of epider- 

 mis from both surfaces, and study the breathing-pores. 



(c) With a low-power study the sori (clusters of spore-cases), 

 using top light only. The sporangia maj^ be seen and their 

 attachment made out in this way in those cases where there 

 is no indusium covering the sorus. 



{d) ]\lake a vertical section through a sorus and stud}' care- 

 fully, looking for the ring of darker cells on the spore cases. 



(e) Gametophytes of ferns may often be found in plant- 

 houses on or in flower-pots near ferns. They may be obtained 

 also by sowing the fresh spores in flower-pots and keeping them 

 in a warm damp place (a greenhouse is best). In a month or 

 two the gametophytes will be full grown. Collect a few of 

 these of various sizes, carefully wash off the dirt from the under 

 side, then mount in water, and examine the untlcr surface for 



