﻿TRUNK STRUCTURE. 



63 



depression outside the main continuous series, must indicate the origin of the 

 pinnule supply. This unique arrangement thus really represents a transition form. 

 It is also probable that the simple closed or Stangerta and Bowenta type must 

 have been more widely present in fossil forms. Hence the closed cycadeoidean as 

 contrasted with the open or omega pattern, characteristic alike of the ancient Cycas 



Fig. 33. — Leaf-base and rachis bundle patterns of various cycadeoidean species as seen in transverse sections. 



1 . Cycadella (Cycadeoidea) ulopiensis, type. S. 339. I cm. distal to insertion of leaf base on cortex. ■ 2. 



2. Cycadeoidea Stillwelli. type. From fractured surface 1.5 cm. distal to cortex. ■ 2. 



3. Cycadeoidea nigra. Cut several centimeters distal to the cortex. Natural size. 



4. Cycadeoidea Macbridei. T. 18. S. 3 18 and 319. Several centimeters distal to cortex. X 2. 



5. Cycadeoidea dacotensis. S. 201. > 2. 



6. Cycadeoidea turrita. S. 24. > 2. 



7. 8. Cycadeoidea superba. T. 147. S. 337 and 338. -2. 



9. Cycadeoidea ingens. type. S. 173. Cut well out on the basal portion of a pinnule-bearing rachis, and hence not 



directly comparable with the other sections. X 2. 



10, II, 12. Cycadeoidea ingens. T. 208. Natural size. From polished surfaces. No. 10 is farthest distal, and 1 2 lies 

 near leaf-base insertion. Rapid increase in number of the bundle; by forking is seen to occur at level of I I and 12, 

 without distinct grouping. 



and the more modern Zamuc^ can not be considered as fundamentally different, 

 although forming a distinction of considerable taxonomic value. The omega type 

 of bundle distribution results in a heavy continuous ridge between the two rows of 

 pinnules, while the closed type would appear to produce closely-set pinnules with 

 the nearly-overlapping bases seen in such forms as Ptilophyllum and Otozamites. 



