284 ORDERS OF FILICALES 



parture in its mode of life acted as a profound stimulus and 

 cooperated in inducing marked variations that were so beneficial 

 in character as to cause the sporophyte to assume large pro- 

 portions and become differentiated into a highly organized plant. 

 The stem elongates through the repeated division of a single 

 apical cell, as in the Bryophyta, but the stem and also the leaves 

 and roots in addition contain vascular bundles and an arrange- 

 ment of tissues already noticed in the higher plants. 



The gametophyte in many of the Pteridophyta is very sugges- 

 tive of the simpler thalloid hepatics. Owing to the fact that it 

 is no longer permanently burdened with the nutrition of the 

 sporophyte, it becomes greatly reduced in size and length of life. 

 In fact, in several of the more specialized ferns, the gameto- 

 phyte may be reduced to a few cells and the entire development 

 may take place within a day. The reproductive organs and the 

 germination of the gametospore are suggestive of the correspond- 

 ing features noted in the Bryophyta. The more important orders 

 of the Pteridophyta are: I. Ophioglossales or Adder Tongue 

 Ferns. 2. Filicales or Common Ferns. 3. Equisetales or Horse- 

 tail Ferns. 4. Lycopodiales or Club Moss Ferns. 



Order 1. Ophioglossales or Adder Tongue Ferns 



112. General Characters of the Sporophyte. — This order con- 

 tains three genera of very primitive ferns which are probably 

 but a remnant of an earlier and widely distributed group. Only 

 two, Ophioglossum and Botrychium, are of common occurrence 

 (Fig. 215). They are of unusual interest because they present 

 many features suggestive of the liverworts and also of the more 

 specialized ferns and seed plants. The sporophyte consists of 

 a short upright stem with thick fleshy roots that are associated 

 with mycorrhiza. The leaves are simple or divided and usually 

 appear singly, ensheathing the apex of the stem. One of the 

 most remarkable features about these ferns is the development 

 in the stems, roots and leaves of the same tissues that we have 

 noted in the higher seed plants. The vascular bundles are usually 

 collateral and in the larger species of Botrychium are arranged 



