92 THE ROYAL SOCIETY OF CANADA 



crowded they are broad, usually reaching across the face of the 

 tracheid. 



That these large primordial pits have originated in the same way 

 as those of the families considered above is proved by a consideration 

 of conservative regions. Fig. 12, Plate II, shows a tracheid from 

 the root of Pinus strobus close to the primary wood. The pits are 

 uniseriate, scattered and enlarged, but well marked rims of Sanio 

 are to be seen clinging closely to their borders. In this primitive 

 region the ancestral condition where the size of the primordial pit 

 has not increased beyond that of the bordered pit is retained. Jeffrey 

 (8) apparently overlooked the rims of Sanio in this region, for he 

 states that in Pinus "bars of Sanio make their appearance late, and 

 not in proximity to the primary wood," a statement which might be 

 considered correct had Jeffrey made the distinction between bars and 

 rims of Sanio. This, however, he did not do. 



A recapitulation of the development of the large, compound 

 primordial pit from the primitive type shown in this figure is exhibited 

 as one passes from the primary wood outward in the roots of various 

 Abietineae. Indications of the fusing of rims end to end occur in 

 a figure of Larix americana root by Thomson (12), and have been 

 observed by the writer in the root of Pinus Lambertiana and Pinus 

 strobus. As one passes out from the centre of the root the primordial 

 pits become larger until the maximum size is reached and the pits 

 and rims have fused to produce a condition such as that illustrated 

 in Fig. 11. 



The primitive rim of Sanio is to be seen in other parts of the 

 Abietineae than the roots. In Fig. 13, Plate III, it is present in a 

 radial section of the secondary wood of the cone of Pinus resinosa 

 close to the primary xylem. The photograph is poor owing to the 

 irregularity of the tracheids in the region, but rims of Sanio are in 

 evidence in close contact with several of the bordered pits. 



In the adult wood throughout the Abietineae, minor variations in 

 primordial pitting are present, though the general type illustrated in 

 Fig. 11 is preserved. In the Cedrus stem the rims were sometimes 

 closely applied to the pits. This was observed in wounded material, 

 and the wounds may account for the primitive character. Near the 

 pith, in this form, the same tendency was observed. The nine species 

 of Pinus investigated all showed the typical specialized form of rim 

 though with variations in staining properties. 



In the Taxaceae the rims of Sanio show evidence of the close 

 relationship of the family to the Pinaceae, for it is evident that the 

 same process of evolution has been followed. In young Dacrydium 



