PTERIDOPHTTA. 227 



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

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

 from both surfaces, and study the breathing-pores. 



(c) With a low power study the spore-dots, using top light only. 

 The spore-cases may be easily seen and their attachment made out 

 in this way in those cases where there is no cover- 

 ing to the spore-dot. 



(d) Make a vertical section through the cluster 

 of spore-cases, and study carefully, looking for the 

 ring of darker cells on the spore-cases. 



(e) Sexual plants of ferns may often be found in 

 plant-houses on or in flower-pots near ferns. They iqj; n 

 may be obtained also by sowing the fresh spores in section of under- 

 flower-pots and keeping them in a warm damp S^'iv"'^ f'p? "*• s 

 place (a greenhouse is best). In a month or two aquilina). 00, 

 the plants will be full grown. Collect a few of yascull^iundles; 

 these of various sizes, carefully wash off the dirt iff. inner flbro-vas- 

 from the under side, then mount in water, and ex- two* ban d a' oi 

 amine the under surface for antherids and arche- fibrous tissue 

 gones (Figs. 128, A, 129, 130). By careful search- p, soft tissue (par- 

 ing young fernlets may be found still attached to of sto^ Mssue""*^ 

 the sexual plant (prothallium), as in Fig. 138, B. 



(/) Collect specimens of Adder-tongue or Moon wort, and compare 

 the structure of the spore-cases with the foregoing. 



{g) Search the borders of lakes, ponds, and slow streams for Pep- 

 perworts, especially species of Marsilia. They may probably be 

 found in every part of the country, although they have rarely been 

 collected. 



Systematic Literature. — Underwood, Our Native Ferns and Their 

 Allies. Gray, Manual of Botany, 678-695, pi. 16-SO (6th edition). 

 Hooker and Baker, Synopsis Filicum. Baker, Handbook of the 

 Fern Allies, 134^149. 



Class 13. EairiSETiNa:. The Horsetails. 



423. In the plants of this class the plant-body of the 

 asexual plant consists of a hollow elongated and jointed 

 stem, bearing whorls of narrow united leaves, which form 

 close sheaths {s, Fig. 136) ; the stem is grooved, and is 

 usually rough and hard from the large amount of silica de- 

 posited in the epidermis. 



