508 



HUTCHINSON'S POPULAR BOTANY 



The Order Osmundaceae is deficient in the indusium, and the ammlus is 

 very greatly modified. The sporanges are borne on certain of the pinnules 



of the fertile frond of which the mesophyll 

 is partly or entirely undeveloped, so that 

 only the sporanges thickly clustered round 

 the midrib are visible. The sporange is 

 not symmetrical : in some species it is 

 shortly stalked, in others sessile. The in- 

 complete contracted annulus is near the 

 apex on one side, and at a little distance 

 from this the sporange splits vertically. 

 The prothallium exhibits a tendency to 

 become dioecious : sometimes all the spores 

 from one sporange produce prothallia 

 that bear antherids only, or archegones 

 only. Some prothallia bear antherids first 

 and archegones later. Often the pro- 

 thallium throws out adventitious shoots, 

 and so propagates itself vegetatively. 



In all these orders of Ferns the verna- 

 tion is circinate, the frond and its divisions 

 being rolled up from the apex. The genera 

 Ophioglossum and Botrychium, often in- 

 cluded in the Class Filices. differ from them 

 in this respect among other differences, 

 their fronds in the incipient stage being 

 folded from the sides. These genera are, 

 therefore, elevated into a separate class, 

 the Ophioglossacese. The upright stem 

 produces only a few leathery fronds, often 

 only one frond. The rachis of the frond 

 is furnished at the base with scaly out- 

 growths, like the so-called stipules found 

 in a tropical order of ferns, the Marattiacese. 

 When the rachis has attained half its final 

 length, it forks, one branch developing 

 into a smooth leafy expansion, furnished 

 with stomates on both surfaces, the other 

 becoming the sporophyll bearing the closed 

 sporanges. These fronds are of very slow 

 growth; in our Moonwort (Botrychium lu.n-' 

 aria, fig. 648), for example, they do not appear above ground until four 

 years after the formation of the bud, their expansion marking their fifth 

 year. The root-stocks are poorly developed, bearing thick neshy root- 



Fio. 648. MOON-WORT (Botrychium 

 lunaria). 



One branch of the frond bears the sporangia, 

 (a) Closed sporanges enlarged. 



