PTEROPSIDA 149 



(called the inner and outer anterior quadrants) and two 

 away from the notch (called the inner and outer posterior 

 quadrants). The outer anterior quadrant ultimately gives 

 rise to the first leaf, the inner anterior to the shoot apex, the 

 outer posterior to the first root, and the inner posterior to 

 the foot. This, at least, is the procedure described in 

 classical studies, but more recently it has been stated that 

 the fate of the four quadrants is not always so clearly 

 defined. ^^ 



Statements that certain characters are primitive and others 

 advanced can be made with more certainty for the Filicales 

 than for any other group in the plant kingdom, because of 

 the large number of fossil representatives that are known. 

 Some of the famiUes had already become widespread by the 

 Mesozoic, while others appeared as long ago as the Car- 

 boniferous. A comparison of these with the rest of the living 

 Fihcales makes it possible to draw up an extensive list of 

 primitive characters for the group as a whole. The following 

 list is based on that of Bower^ (as modified by Holttum^^) 

 with additions by Stokey.^^ 



Rhizome — slender, creeping, dichotomous, with fronds in 

 two ranks on its upper side, protosteUc, covered with 

 hairs. 



Fronds — large, amply branched, dichotomous and of un- 

 limited growth, the stipe (petiole) receiving a single leaf 

 trace, the ultimate pinnules narrow and with a single 

 vein; venation without anatomoses (i.e. *open'). 



Sort — containing few sporangia, terminating a vein. 



Sporangia — relatively large, with stout stalk, without a 

 specialized annulus, developing and dehiscing simul- 

 taneously to liberate a large number of spores. 



Spore germination — giving a plate rather than a filament 

 of cells. 



Gametophyte — relatively large, thalloid, with a thick mid- 

 rib, slow to develop. 



