90 THE ROYAL SOCIETY OF CANADA 



second tracheid from the left are shown bars incompletely fused, 

 though the ends are not forked as in the very suggestive example 

 illustrated in Fig. 7. The stem of Thuja shows a similar condition 

 in regions, such as the ends of tracheids, where biseriate pitting is in 

 evidence. The typical condition in the stem, however, is illustrated 

 in Fig. 9, Plate II, where the pitting on the rather irregular tracheids 

 is uniseriate and the rims and bars are so perfectly fused together as 

 to give no hint of their compound nature. At the right of the figure 

 is shown a little of the summer wood with its narrow lumina and small 

 pits. The rims of Sanio do not come out clearly in summer wood, 

 owing probably to the heavy lignification, but they may be seen 

 between the second and third pits from the top, to be of the same 

 essential nature as those of the spring wood. 



A study of several other members of the Cupressineae revealed 

 no great variation in structure from the points already mentioned. 

 In the root of Thuja Standishii indications of incomplete fusion of 

 the rims were found, while in the stem the specialization is apparently 

 complete. Material of Cupressus Benthami seedling, and various 

 regions of Thuja plicata, Thuja orienlalis, and five species of Juniperus 

 was available and in all of these the development of the compound 

 bar is, as a rule, complete. Doubtless relics of the ancestral characters 

 are present in the most conservative regions of some or all of these 

 forms, but they are less plentiful than in those which have been 

 described more in detail. 



There is a fairly general tendency for the bars to appear less 

 strongly marked in stem than in root wood, either through their 

 partial lignification or for some unknown cause. They are, however, 

 sufficiently definite to indicate clearly their homology with those 

 illustrated in the stem of Thuja (Fig. 9). Even where, as in some 

 species of Juniperus (e.g., /. communis, J. davurica and /. occidentalis 

 stems) they have become shortened, it is quite apparent, even without 

 the evidence furnished by the roots, that they border enlarged pri- 

 mordial pits such as have been described. 



Passing to the Taxodineae, evidence of the development from the 

 Cycadean-Aruacarian type of primordial pit and rim of Sanio to 

 the more specialized form is again found. Fig. 10, Plate III, is a 

 radial section of the root of Taxodium distichum. The pitting here 

 is less scattered but there is evidence of a considerable amount of 

 elimination. In the two middle tracheids there has been a reduction 

 at least from the triseriate to the biseriate condition and the bordered 

 pits have not enlarged sufiiciently to fill the space left by the central 

 row which was eliminated. There has not been room for the pri- 



