[sifton] bar of SANIO IN GYMNOSPERMS 91 



mordial pits to enlarge to a great extent vertically but they have 

 done so in a horizontal direction, and fused to form long, narrow pits 

 bordered above and below by straight bars of Sanio passing from 

 side to side of the tracheid. That these bars are compound structures 

 is shown in some cases by constrictions which divide them into three 

 parts corresponding to the ancestrally triseriate primordial pitting. 

 This condition is marked in the seventh bar from the bottom of the 

 second tracheid from the right and in the sixth from the bottom 

 of the tracheid to the left of this. It is to be seen also in others. 

 In this triseriate condition it is remarkable that divisions between 

 the bars, crowded end to end as they are, should be evident even to 

 the degree shown. The divisions are delicate and difficult to photo- 

 graph, but can be clearly seen in the section. 



As shown in the photograph, uniseriate bordered pits are also 

 found in the root of Taxodium, though to a less extent than in the 

 stem, which is illustrated in Fig. 14. The bordered pits are larger 

 in proportion to the width of the tracheid, but not large enough to 

 fill the compound primordial pits, which are bounded above and 

 below by well marked rims whose components have become perfectly 

 fused. 



In other members of the Taxodineae which were available for 

 study the pits even in the roots are more reduced in number, there 

 being a tendency toward the uniseriate condition. In these the 

 bordered pits are inserted typically in broad primordial pits which 

 they do not completely cover, but whose rims have lost any indication 

 of their compound nature. The ancestral condition is indicated in 

 very conservative regions by the presence of bordered pits completely 

 covering the primordial pits and with rims of Sanio closely attached 

 to their borders. This condition will be again referred to when the 

 Abietineae are considered. It has been observed in the seedling 

 root of Cunninghamia sinensis, and in the root of Sciadopitys verticillata 

 near the primary wood. 



Fig. 11, Plate III, is a radial section of the stem of Abies amabilis 

 and illustrates typical Abietinean pitting. The bordered pits are 

 large as compared to those of the Cycads and Araucarians, and are 

 placed in primordial pits which are still larger, resembling in every 

 respect those whose development has been traced in the Cupressineae 

 and the Taxodineae. The rims of Sanio do not normally touch the 

 borders except where the pitting is somewhat crowded and even here 

 they pass beyond the individual bordered pit horizontally. In other 

 words, the primordial pits to which the rims attach themselves have 

 increased greatly in height wherever there is room, and even where 



