;60 



OEGANOGRAPirr, 



containing spores in their interior. In a very few cases capsules 

 have been observed on the upper surface of the fronds, as in 

 Acrostichum. The capsules are arranged in little heaps, which 

 vary much in form, called sori {figs. 783 and 784, s), and are 

 either naked, as in Polypodium {fig. 783), or covered by a thin 

 membranous layer continuous with the epidermis, which is called 

 the indiisium or involucre, as in Nepkrodium Filix-mas {fig. 7^4:). 

 Sometimes the capsules are so densely compacted that no inter- 

 vening parenchyma can be distinguished— the latter being de- 

 stroyed by the excessive development of the former ; in such cases, 

 the capsules, instead of being collected in sori on the back of 

 the fronds, appear as little bodies arranged in a spiked manner 

 on a simple or branched rachis, as in Osmunda {fig. 785), 



Fig. 784. 



Fig. 785. 



Fig. 783. A portion of the frond of the rommon Polypody (Pohjpodium 

 viih/tire) showing two sori springing from its reins. The sori are 

 naked, and consist of a number of capsules, gp.in which the spores are 



contained. Fig. 784. Portion of the frond of the male-fern (Nephro- 



diinu FiH.r-ma»), with two sori, s, s, covered by an indnsium oriiivo- 



lucie. Fig. 785. Portion of the frond of the Royal or Flowering-fern 



(Oamuvdd. regalis), with its capsules arranged in a spiked manner on a 

 branched rachis. 



The capsule is a little cellular bag or case {fig. 786, s), usu- 

 ally stalked, p, and more or less completely surrounded by a ring 

 ov\mmdus; this ring is frequently elastic, and thus causes the 

 bursting of the capsule when ripe, and the escape of its spores. 

 In some Ferns the ring is imperfect, and in others it is alto- 

 gether wanting ; hence Ferns provided with a ring are called 

 annulate, while those in which the ring is absent are said to be 

 cxannulate. 



The spores are usually somewhat angular in form, and have 

 two coats like pollen-cells ; and like them also, the outer coat, 

 Avhich has a yellowish or brownish colour, is either smooth or 

 furnished with little points, streaks, ridges, or reticulations. In 

 germination {fig. 787), the inner coat is first protruded in the 



