REPRODUCTION. 51 



segments (pinnae) corresponding to those of Polypo- 

 dium are cleft entirely to the main stalk,, the pinnae 

 (fig. 1 7) being pinnatifid ; and the segments of the 

 pinnae or the pinnules (fig. 18) are oblong, obtuse, and 

 saw-edged (serrate) . In all botanical works the fronds 

 are incorrectly said to be bipinnate. 



The sori are brown, kidney-shaped (fig. 18), and 

 differ from those of Polypodium in being covered by a 

 thin membrane (indusium), which is fixed to the frond 

 at the notch. 



Scoloperi drium vulgdre (PL II. fig. 19), the Hart's- 

 tongue Fern, is common in hedges and on moist banks. 

 Its fronds are simple or undivided, strap-shaped, 

 heart-shaped at the base, and narrowed to a point at 

 the apex. The sori (fig. 20) are brown, narrow, 

 longish (linear), and transverse or slightly oblique. 

 The indusium is cleft down the middle, so as to form 

 a longitudinal fissure or suture. 



Reproduction. The spores of the ferns (PL II. fig. 

 12 a] resemble in appearance the seeds of flowering plants 

 on a small scale. They are usually brown, covered on 

 the surface with little tubercles or other markings, 

 and when kept on a slide in a moist atmosphere, as 

 over a saucer of water covered with a bell-glass, they 

 germinate. When this takes place, one or more 

 short, brownish, hair-like radicles emerge from one 

 part of the surface (PL II. fig. 13), and a process con- 

 taining chlorophyll issues from an adjacent spot. As 

 growth proceeds, the latter by cell-division gives rise 

 to a flattened two-lobed leafy cotyledon-like body or 

 prothaHium (irpb, before, 0aXXo9, leaf), with nume- 

 rous rootlets springing from the base of the lobes. 

 The prothallium is of a peculiar dull-green colour, 

 different from that of the young frond which is subse- 

 quently formed. This arises from the absence of 

 stomata and intercellular passages containing air ; for 

 the air in these passages of leaves and petals contri- 

 butes greatly to the production of the brightness of 



