GENERATIVE ORGANS OF FERNS. 



355 



than tliose yielded by the rarest exotics ; and it is in every respect 

 a most valuable training to the young, to teach them how much 

 there may be found to interest, when looked for with intelligent 

 eyes, even in the most familiar and therefore disregarded speci- 

 mens of Nature's handiwork. 



219. The spores (Fig. 145, a) set free by the bursting of the 

 thecse, usually have a somewhat angular form, and are invested 

 by a yellowish or brownish outer coat, which is marked, very- 

 much in the manner of pollen-grains (Fig. 187), with points, 

 streaks, ridges, or reticulations. When placed upon a damp sur- 

 face, and exposed to a sufficiency of light and warmth, the spore 

 begins to "germinate," the first indication of its vegetative ac- 

 tivity being a slight enlargement, which is manifested in the 



Fig. 145. 



Development of Prothalliurn of Pteris seiTutatti: — A, epore set free from the theca;'-B, spore begin- 

 ning to germinate, putting forth the tubular prolongation a from the principal cell, b ; — c, first formed 

 linear series of cells; — u, prothallium taking the form of a leaf-like expansion ; a first, and h second 

 radical fibre; c, d, the two lobes, and e the indentation between them;/,/, first formed part of the 

 prothallium ; g, external coat of the original spore ; A, h, antheridia. 



rounding off of its angles ; this is followed by the putting forth 

 of a tubular prolongation (b, a) of the internal cell-wall, through 

 an aperture in the outer spore-coat ; and by the absorption of 

 moisture through this root-fibre, the inner cell is so distended, 

 that it bursts the external unyielding integument, and soon 

 begins to elongate itself in a direction opposite to that of the 

 root-fibre. A production of new cells by subdivision then takes 

 place from its growing extremity ; this at first proceeds in a single 

 series, so as to form a kind of confervoid filament (c) ; but the 

 multiplication of cells by subdivision soon takes place transversely 

 as well as longitudinally, so that a flattened leaf-like expansion 

 (d) is produced, so closely resembling that of a young Marchantia 

 as to be readily mistaken for it. This expansion, which is termed 

 the prothallium, varies in its configuration in different species ; 



