3 I2 



THE ANATOMY OF WOODY PLANTS 



that the pitted tracheids nearest to the primary wood are entirely 

 without bars of Sanio, which make their appearance only at an 

 interval from the protoxylem. The pitting to a large extent is 

 alternate. It is very generally admitted by competent judges 

 at the present time that the Ginkgoales are derived from cordaitean 

 ancestry, and it is accordingly highly interesting to find in the 



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FIG. 222. Longitudinal view of the tracheids in the peduncle of a seed in Ginkgo. 

 To the right is shown the arrangement of the tracheids in the mature wood. 



organization of vegetative and reproductive axes evidence based 

 on the pitting and distribution of the bars of Sanio favorable to 

 such an opinion. Farther away from the primary wood the 

 secondary tracheids quickly develop the opposite pitting and 

 bars of Sanio characteristic of the mature wood. It is clear from 

 the figure, moreover, that the tracheids of the primary wood are 

 quite devoid of structures of the nature of the bars of Sanio. It 

 is well to emphasize the conditions found in the organization of 

 the root and reproductive axis of Ginkgo, because there prevails 



