[sifton] bar of SANIO IN GYMNOSPERMS 89 



ment is not to be taken as an indication of supposed phylogenetic 

 relationship. Ginkgo is reserved to the last because it is regarded as 

 a special form due to certain features of arrested development. 



Fig. 7, Plate II, a radial section of secondary wood from the 

 root of Chamaecyparis ohtusa {Reiinospora lycopodioides) illustrates 

 an advanced condition approaching the most specialized in the higher 

 Gymnosperms. With the elimination of large numbers of the pits, 

 which covered the whole radial surface of the tracheids of the lower 

 Gymnosperms, comes the possibility of enlargement for those that are 

 left. In the form under consideration this enlargement has taken 

 place to a very noticeable extent. The primordial pits, outlined by 

 their rims of Sanio, have here increased to a greater area than have 

 the bordered pits, and the rims of Sanio are thus no longer in contact 

 with the latter. The point with regard to these, however, is that 

 while the bordered pits of the secondary wall have been reduced to a 

 uniseriate condition the same is not true of the primordial pits. In 

 each case the bordered pit appears superficially to be inserted on a 

 simple primordial pit reaching from side to side of the tracheid, but 

 a consideration of the rims of Sanio leads to a different conclusion. 

 At the centre of the second tracheid from the left, for example, the 

 bars are plainly in horizontal pairs with a clear space separating the 

 ends. The primordial pits have enlarged, overlapped and fused 

 horizontally, but the end to end fusion of their rims of Sanio is not 

 yet completed, and the gaps indicate the compound origin of the 

 large primordial pit. The forking ends of the short bars show that 

 each is a true bar of Sanio, composed of two vertically fusing rims. 

 In other parts of the section the fusion of bars is complete. In the 

 second bar from the top of the third tracheid from the left the bars 

 are completely united, while the compound nature of the primordial 

 pit is indicated by the imperfectly fused bars below it. In the stem 

 of Chamaecyparis complete fusions of the bars are the rule. 



It is generally admitted that the ancestral pitting for this and 

 other conifers is multiseriate, and each of the shorter bars discussed 

 above would thus be formed of two or more which have overlapped 

 and fused. This overlapping accounts for the thickness of the bars 

 in this and higher forms, where it is more pronounced than in forms 

 like the Cycads and Araucarians. 



Chamaecyparis is not the only genus of the Cupressineae which 

 indicates the mode of formation of the complex bar of Sanio of the 

 higher forms. In the root of Thuja, in regions of biseriate pitting, 

 it is often in evidence. Fig. 8, Plate II, illustrates a fairly common 

 condition in the root of TJwja occidentalis. Near the centre of the 



