43° 



BOTANICAL GAZETTE 



[DECEMBER 



lower central part of the figure. The uniseriate and scattered 



e> 



formed 



pits, as in the Cycads. The only evidence of this in the fossil 

 section, however, is the decreased size of many of the pits in the 

 region of elimination. A careful examination of fig. 5 will make 

 this point clear. 



It will be seen from the foregoing account that the Cycads, 

 besides giving indication of the mode of formation of the bordered 

 pits from the scalariform type, afford valuable data on the inter- 

 pretation of the arrangement of pits. The elimination in these low 



I 



b 



Fig. 1. — Cycas revoluta: radial views of different regions of tracheid from stem; 

 a, end of tracheid; b> normal pitting at contact of two tracheids; c, pitting in contact 

 with medullary ray. 



forms shows no indication of following a definite law, but proceeds 

 promiscuously, giving rise to all the various types of pitting. It 

 is practically restricted, however, to the middle part of the tracheid, 

 the terminal portions and those parts in contact with the ray cells 

 remaining multiseriate. 



The terminal and ray pitting of the tracheids has always 

 remained primitive in another respect. This is indicated in text- 



stem 



In 



this figure a represents the terminal pitting, b the ordinary pitting, 



tracheid. The pits and their 



same 



pores are longer in a and c than in b. The pores often extend 



