- 



A 



1920] SIFTON—CYCADS 



431 



beyond the borders in a and c, and thus recall the condition where 

 pits are forming on scalariform elements (fig. 3). Many of the 

 pores were measured for definite comparison, and the tracheid 

 figured does not exaggerate the difference in pit and pore lengths. 

 Ray pitting on Dioon spinulosum secondary stem wood is shown 

 I in fig. 9. Here also the multiseriate pitting is present, accom- 



panied by the elongated pore. The left hand tracheid of fig. n 

 shows the same type of pore, where a vertical parenchyma cell is 

 in contact with a tracheid. Evidently the primitive type of pore 

 occurs wherever a tracheid is in contact with any type of paren- 

 chyma cell. Similar primitive features have been recorded by 

 Thomson (ii) in Araucarian ray pitting. 



Tertiary thickenings are common on the tracheid walls, taking 

 the form of spirals or scalariform bars with long shallow pits 

 between. They occur whether bordered pits are present or not, 

 and often traverse the region of the border itself, but have never 

 been observed to cross the pores. Penhallow regarded such 

 thickenings as relics of the ancestral manner of deposition of the 

 cell wall, a view which is strengthened by their presence in these 

 low forms. 



Bars or rims of Sanio 



Considerable importance was attached for some years to the 

 presence or absence of " bars " or "rims " of Sanio. Miss Gerry (3) 



them 



Conifers 



distinguishing 



between both fossil and living Araucarians and other coniferous 

 forms. Jeffrey (6) and Thomson (ii), however, in practically 

 simultaneous publications described bars from the transitional 

 region of the pitting in the cone axis of an Araucarian. Thi 

 Jeffrey interpreted as evidence of the derivation of Araucarians 

 from the Abietineae. He recognized that this evidence would be 

 invalid if all primitive types of pitting had bars of Sanio, and 

 looked for them in primitive regions of Cycas but failed to find 

 them. Their presence here was described later by the writer (10), 

 and invalidates his conclusions. Jeffrey's misstatement has no 

 loubt been responsible for the exaggeration of the importance of 



