SECTION 17.] 



PTERIDOPnYTES. 



161 



like cavities, and fertilise the cell. This thereupon sets up a growth, forms 

 a vegetable hud, and BO develops the new plant. 



491. An essentially similar process of fertilization has been discovered 

 in the preceding and the following families of Pteridophytes ; but it is 

 mostly subterranean and very difficult to observe. 



492. Club-Mosses or Lycopodiums. Some of the common kinds, 

 called Ground Pine, arc familiar, being largely used for Christmas wreaths 

 and other decoration. They are low evergreens, some creeping, all with 

 considerable wood in their stems: this thickly beset with small leaves. In 

 the axils of some of these leaves, or more commonly, in the axils of pecu- 

 liar leaves changed into bracts (as in Fig. 511, 512; spore-cases appear, as 

 roundish or kidney-shaped bodies, of firm texture, opening round the top 

 into two valves, and discharging a great quantity of a very tine yellow 

 powder, the spores. 



493. The Selaginellas have been separated from Lycopodium, which 

 they much resemble, because they produce two kinds of spores, in sepa- 

 rate spore-cases. One kind (Microspores) is just that of Lycopodium; 

 the other cousists of only 

 four large spores (Macro- 

 spores), in a spore-case 

 which usually breaks in 

 pieces at maturity (Fig. 

 513-515). 



494. The Quill worts, 

 Isoetes (Fig. 516-519), 

 are very unlike Club Mos- 

 ses in aspect, but have been 

 associated with them. They 

 look more like Rushes, and 

 live in water, or partly out 

 of it. A very short stem, 

 like a conn, bears a cluster 

 of roots underneath ; above 

 it is covered by the broad 

 bases of a cluster of awl- 

 shaped or thread-shaped 



leaves. The spore-eases 



are immersed in the bases 



of the leaves. The outer 



leaf-bases contain numerous macrospore 



merable microspores, 



495. The Pillworts {Marnlia and Ptiularia) an 



the inner are filled with iiinu- 



low aquatics, which 



Fio. 520. Plant of Manilla quadrifoliata, reduced in Rise; at the right ■ pair of 

 ■poro-carps of about uatural size. 



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