WATER FERNS 259 
Maidenhair of the North (Adiantum pedatum), and of 
the South (A. capillus-veneris), 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 Q 
rise respectively to antheridial, and arch- 
egonial gametophytes. The Marsilias are Fra. 136.— 
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. 
(6b) 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 may be seen and their 
attachment made out in this way in those cases where there 
is no indusium covering the sorus. 
(d) Make a vertical section through a sorus and study 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 under surface for 
