520 A TEXTBOOK OF THEORETICAL BOTANY 



apex. The sporangia are large, are not constant in regard to their formation 

 on the leaf margin or the leaf surface and are not grouped in sori or protected 

 by an indusium. Furthermore they develop more or less simultaneously. 

 All these are primitive characters and justify the inclusion of the family 

 in Bower's Sitnplices. 



The Osmundaceae occupy an intermediate position between the Lepto- 

 sporangiatae and the Eusporangiatae, though they are usually included in 

 the former group. This indeterminate position is due to the variations 

 in the development of single sporangia, even on the same plant, some forming 

 a pyramidal archesporial cell, as in the Leptosporangiatae, others a cubical 

 cell, as in the Eusporangiatae. The sporangia are derived from more than 

 one cell of the sporophyll which is a character of the latter group. 



The Ferns of this family are mostly large plants with perennial stems, 

 which are embedded upright in the soil with only the crown exposed. They 

 may branch dichotomously in old specimens and form large masses of stems 

 up to a metre in diameter and sometimes several feet in height. The leaves 

 are deciduous and when they die down in autumn they form a blanket over 

 the crown of the plant, persisting through the winter in the dry state. 



The Osmundaceae occur in all parts of the world, but Todea is confined 

 to South Africa and Australia. In the tropics Osmunda is confined to 

 mountain ranges and does not grow at lower levels. They extend backwards 

 in time to the Palaeozoic period, and were well developed in the Jurassic. 

 They show connections with a primitive group of Ferns, the Botryopteri- 

 daceae, which were abundant in the Carboniferous, and they have probably 

 been derived from them. 



In Todea the fertile leaves are morphologically identical with the sterile 

 leaves, but in Osmunda the fertile upper pinnae of the leaves have practically 

 no lamina and bear sporangia all round, thus appearing very different from 

 the lower sterile portions, which has led to their being popularly called 

 " Flowering Ferns." 



We shall describe as a type the species Osmunda regalis. 



Osmunda regalis (The Royal Fern) 



Osmunda regalis is a native of Britain, being found in boggy places chiefly 

 in the m.oist regions of the West and North. It is not uncommon, but seldom 

 occurs in large numbers. It has a wide geographical range, from Sweden 

 to South Africa and from Canada to the Argentine. The plant is perennial 

 and grows to a large size, with leaves which may be up to 6 ft. long (Fig. 516). 

 They last only for one season, but their bases remain as persistent coverings 

 around the stem, as in Dryopteris. There are distinct sterile and fertile leaves, 

 and the latter are produced first and stand erect, while the sterile leaves 

 arch outwards around them (Fig. 517). Each leaf is bipinnate, and in the 

 fertile leaves the five or six pairs of pinnae nearest the top of each leaf are 

 reduced to little more than their midribs and bear masses of brown sporangia 

 all over their surfaces, which makes them rather conspicuous objects. 



