114 



CELLULAR CONSTRUCTION 



[CH. 



the roots have been examined by Schwendener. The roots are thicker than 



those of any other Hving Ferns, and they contain as a rule four truncated 



prismatic initials, corresponding in 



number and form to those occasionally 



seen in roots of Osmtmda and Todea 



(Fig-, no, E). Here again the centre 



of construction is deeply sunk. It is 



the sporangia, however, that give the 



most marked character to the Marat- 



tiaceae. These are much more massive 



than in the Osmundaceae. They arise 



by outgrowth of a large number of 



cells, the cleavages of which form a 



coaxial system (Fig. 113). 



The comparisons relating to the 



Ophioglossaceae are less clear. Their 

 stems and roots have each a single 



initial cell, though all are massive in 



construction. The leaves of the young 



plant of Botrychium are described as 



having a single initial : but neither 



here nor in Ophioglossum or Helmin- 



thostachys is there any regular apical 



or marginal segmentation in the adult 



leaf comparable with that in Leptosporangiate Ferns. The development of 



the sporangium of Botrychium and HelmintJwstachys conforms generally to 



the Marattiaceous type. It is eu-sporangiate, springing from a numerous body 



of cells, with cleavages on a coaxial system. In Ophioglossum the sporangium 



is more massive than in any of the other Filicales. (See Chapter xiil.) 



Upon the facts thus stated it is possible to seriate the main groups of the 

 Filicales according to their apical meristems, and the segmentation of their 

 sporangia. At the one end of the series will be those in which the cleavages 

 of the initial cell follow a strict and relatively simple rule, as is seen to be 

 the case in the Leptosporangiate Ferns. At the other end those where more 

 than a single initial cell is commonly present, and the cleavages are less simple 

 and regular. This is the case with the Eusporangiate Ferns, most typically 

 in the Marattiaceae, and with less regularity in the Ophioglossaceae, while 

 the Osmundaceae occupy an intermediate position. This series follows and 

 indeed indicates the general constitution of the plants in question. For the 

 Eusporangiate Ferns are relatively massive plants, and typically possess 

 leathery leaves, fleshy axes, and thick roots: all their vegetative parts thus 

 according with the robust type of their sessile sporangia. The Leptospo- 



Fig. 113. Scheme of construction of the coaxial 

 or Marattiaceous type of root. ^^4 = common 

 axis; a, « = anticlinal curves; /, /=periclinal 

 curves. Compare Fig. no, A. 



