ACROOENS—COVERED SPORES. 



37 



Fig. 34, — Venns Maidenhair (Adiantnm Capillua-Veneris). 

 Spores under edge of fronds, at ends of veins. 



fossil representatives than any other Order, not excepting the Pines ; 

 upwards of two hun- 

 dred species are found 

 in the coal - measures 

 of Europe and North 

 America. 



66. Alternate 

 Generation, or Di- 

 genesis (two crea- 

 tions), is a char- 

 acter of the Ferns 

 and the allied 

 Orders (which fol- 

 low). The spores 

 are produced on the 

 fronds by Parthe- 

 nogenesis (virgin 

 parentage). But 

 the spore thus pro- 

 duced is in a sort of preparative state; when planted, it 



sprouts into a monoe- 

 cious prothallus, which 

 is foliaceous and emar- 

 ginate at tip. This pro- 

 thallus (Fig. 36) devel- 

 ops the bisexual organs, 

 archegonium (ao) and 

 antheridium (an). These 

 behave like those of 

 Vaucheria and other 

 genera in the Orders 

 already described ; they 

 produce an embryo 

 capable of growing up 

 into a fern; but even 

 this embryo is still a 

 simple spore without 

 differentiation into 

 special parts or or- 

 At maturity it sprouts into the true fern, 

 continues during its life of from one to sixty 



Pifl. 35. — Hart's-tongue (ScoJopen(1rinm vuJgare). 

 Spores on veins, on under surface of fronds : a, 

 sporc-caee ; b, same open, showing its elastic ring. 



gans. 

 which 



