[sifton] bar of SANIO IN GYMNOSPERMS 97 



7. The compound nature of these broad primordial pits is in- 

 dicated in conservative regions of several forms by the incomplete 

 horizontal fusion of the bars and rims of Sanio. 



8. In specialized woods the rims or bars connected with these 

 fused primordial pits have also completely fused, and probably over- 

 lapped to form a heavier bar than in the lower forms. 



9. There was a final tendency for the compound primordial pits 

 to become narrowed vertically while retaining their horizontal breadth, 

 which probably led to the condition in the lower Dicotyledons. 



10. In Ginkgo, the elimination of pitting and the subsequent 

 enlargement of primordial pits did not proceed so far as in higher 

 forms. As a result this form is particularly rich in indications of 

 the mode of origin of the compound rims and bars of Sanio. 



To Professor R. B. Thomson, under whose supervision this work 

 was carried out, I am indebted for advice and encouragement, and 

 for a copious supply of material from his collection. 



Botanical Laboratories, 

 University of Toronto, 

 May 31st, 1922. 



7— E 



