106 BOTANICAL GAZETTE [AUGUST 
fusion of rays eliminated a row of tracheids without replacement by 
parenchyma. ‘The tracheids were simply “pinched” out, only the 
parenchyma cells continuing. Ina few cases, even after true marginal — 
ray tracheids had been formed as above indicated, the rays drew 
together and fused, with the result that the marginal ray tracheids 
were “pinched” out. = 
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Fics. 6, 7.—Fig. 6, P. resinosa: young root; illustrating the formation of a 
double row of ray tracheids; fig. 7, P. resinosa: young root; formation of a wholly 
tracheidal ray, and its transformation into a parenchymatous one. 
The origin of the marginal and interspersed ray tracheids and 
their relationship to the fusion of rays have been described. The 
more complicated case of the formation of two rows of tracheids on 
the margin of a ray is partly illustrated in fig. 6. At the left, toward 
the pith, are two rows of transitional tracheids touching end to end. 
Beyond the figure, nearer the medulla, these have been formed from @ 
single row of longer tracheids. Toward the cambium the row on thes 
7 
