358 Causes and Course of Organic Evolution 



highest flowering pkmts or Angiospermia. Varied connecting 

 hnks, therefore, between the higher carboniferous Cordaitales 

 and evolving gnetal and angiospennic branches might well 

 be expected to occur in the fossil state throughout the pennian 

 fonnation. But it is a striking coincidence that the pennian 

 rocks, which we would expect to yield varied and important 

 connecting links between the Amphibia and Mammalia as 

 well as other higher vertebrates, are as poor relatively in these 

 as they are in the plant links now desiderated. 



Dependence must therefore be placed largely on the three 

 very different and yet interrelated genera, Ephedra, Gnetiivi, 

 and Wehcitschia that may well stand as types of three great 

 gnetal families. The stem of these shows, as in Ephedra, 

 close agreement in growth with that of the Casuarinete or 

 Shea oaks; or, as in Gnetum, a combination of cordaital details 

 with those now seen in curvembryonal dicotyledons like Chen- 

 opodiacese and Nyctaginacese ; or, as in Wehvitschia, a parting 

 of the cordaital way that might lead either to monocotyledons 

 or dicotyledons. 



Histologically all three are of great interest, for the elements 

 that make up the secondary wood consist in largest part of 

 porous fibers or tracheids as in the Cordaitese; but the pores 

 become fewer, less prominent, and smaller, thus indicating 

 gradual approach to the fibers of angiosperms. In smaller 

 part the wood is made up of pitted tubes or vessels, that in 

 aspect and in disposition amongst the fibers strikingly recall 

 the pitted vessels of angiosperms. The reduced opposite 

 scale leaves of Ephedra, the amj)le net- veined opposite leaves 

 of Gnetum, and the long leathery parallel- veined leaves of 

 Welwitschia suggest transition stages from Cordaitales to the 

 Angiospermia, such as no other series present. 



In floral structure these three genera show striking advance 

 on cordaital and even on average gymnospermic flowers, at 

 the same time that they present very exact angiospennic 

 details. For, in addition to showing transitions from bracteolar 

 to what can appropriately only be called floral leaves, they 

 exliibit in their sub-hennaphrodite (Welwitschia) or diclinous 



