3 io 



THE ANATOMY OF WOODY PLANTS 



mode of dehiscence; but, in view of the strong development of 

 transfusion tissue in the foliar organs of the group under discus- 

 sion, a clear feature of distinction from the Cycadales and Cyca- 

 dofilicales (in both of which the microsporangia are ectokinetic), 

 it is somewhat probable that the pollen sacs owed their dehiscence 

 to a layer of tracheary origin. The seeds of Cordaites have been 



FIG. 221. Transverse and longitudinal sections of a leaf bundle in Cordaites 

 principalis. 



anatomically investigated by Renault and they possessed a well- 

 marked pollen chamber. A more complete knowledge of the 

 reproductive structures of cordaitean forms and of the types 

 which connected them in the more remote Paleozoic with filicinean 

 ancestors is much to be desired. 



The Ginkgoales are represented by a single living genus, but 

 were extremely abundant in the Mesozoic and are thought to 

 have been continued into the Paleozoic by the somewhat problem- 

 atical genus Whittleseya. Unfortunately our anatomical knowledge 

 of the group beyond that supplied by the investigation of the 



