74 



VASCULAR CRYPTOGAMS 



development, the parenchyme of the fertile (apical) part of the leaf, 

 giving the appearance of a panicled or thyrsoid inflorescence. The 

 sf orange is usually stalked, and has an elliptical form, or that of a battle- 

 dore or racket-bat. The sides are commonly thin and membranous, and- 

 the sporange dehisces either longitudinally or transversely, generally from 

 the elasticity of an annulus or ring of brown thick-walled cells running 

 along or across it. The position of this annulus, and its more or less 

 complete development or entire absence, are useful characters in the 

 subdivision of the class. In the Marattiaceae the sporanges are of 

 altogether different origin, being developed from h)rpodermal masses of 

 cells ; and transitional forms occur between the two. The spores are 



minute, very commonly re- 

 niform, or often nearly 

 cubical, resembling pollen- 

 grains in structure, usually 

 furnished with two coats, 

 an eocospore and endospore, 

 the latter of which is some- 

 times double, and the 

 former generally marked 

 with papillse, reticulations, 

 &c. 



A more minute descrip- 

 tion must now be given of 

 the structure and peculi- 

 arities of the various organs. 

 The great distinguishing 

 feature which characterises 

 the development of the 

 stem of ferns, as contrasted 

 with that which occurs in 

 all Flowering Plants (Gym- 

 nosperms and Angiosperms), is the presence of a single apical cell, 

 from which the whole of the growing point or apical meristem origi- 

 nates, and which may therefore be recognised as the parent-cell of the 

 whole of the tissue subsequently formed. This apical cell is usually 

 wedge-shaped in creeping stems with a bilateral structure, a three-sided 

 pyramid in erect or ascending stems. The growing apex of the stem is 

 frequendy completely hidden in the youngest leaf-bud, but in other species' 

 there is a considerable intervening space. In some Hymenophyllacese 

 leafless prolongations of the stem assume the appearance and the function 

 of roots. As contrasted with Flowering Plants, especially Exogens, the 

 stem of ferns is characterised by the small extent to which it branches ; 



Fig. sz.— Diagram of tip of leaf of Ceraiopteris thaiic- 

 iroides Brongn. S, apical cell ; Z, lateral lobe of leaf. 

 (After Kny.) 



