CHAPTER XIII. THE PTERIDOPHYTA. 



355 



gia are unstalked, provided with an annulus that runs transversely 

 and dehiscence takes place longitudinally. In the Marattiaceae 



the sporangia constituting a sorus 

 grow together, forming a compound 

 sporangium, and in Ophioglossum the 

 sporangia occupy cavities in the in- 

 terior of the leaf near its margins. 

 See Fig. 562. 



Order B. The Rhizocarpeae 

 or Pepperworts. In this order the 

 spores are of two kinds, borne in 

 separate sporangia. Some produce 

 single, large macrospores ; others, 

 much smaller microspores in con- 

 siderable numbers. Both kinds of 

 spores produce very rudimentary 

 prothallia which project but little 

 from the wall of the germinating 

 spores. Those developed from mi- 

 crospores produce antherozoids only, 

 while those which are developed 

 from macrospores produce arche- 

 gonia only. 



The order is a small one, con- 

 sisting of two sub-orders, the Sal- 

 viniaceae and the Marsiliaceae, each 

 represented by but a few species. 



In the Salvinias, the microspore, 

 in germinating, produces a short fila- 

 ment composed of three cells ; the 

 one at the apex, and the one just 

 back of it, are shorter 

 than the basal one. The 

 contents of the two for- 

 mer break up into anther- 

 ozoids, while the latter 

 must be regarded as a 



Fig. 562. —Ophioglossum vulgatum. A, entire plant; f, fruiting portion of leaf. B, part 

 of fruiting portion of leaf, magnified, s, rounded portion of margin, containing in its interior 

 a sporangial cavity, as shown below at s/, where a portion has been cut away so as to 

 show the internal structure. 



