426 BOTANICAL GAZETTE [December 



Jeffrey is more conservative than many others in his estimate 

 of the significance of pitting, but considers that it is of distinct 

 value in classification when its character in all parts of the plant is 

 considered. On this ground, in his work on the Araucarineae, he 

 accepts the presence of opposition pitting in the cone axis, and 

 scattered pits in the seedlings, as denoting descent from an Abie- 

 tineous type. He has neglected the character of the pitting in 

 primitive forms such as the Cycads, however, and his interpretation 

 is not in harmony with the facts which these forms disclose. This 

 was done, notwithstanding the fact that as early as 1840 Don (2) 

 recognized the value in phylogeny of the study of Cycads. He 

 carefully worked over the character of tracheids by such methods 

 as were in vogue at that time, and agreed with Me yens, a still 

 earlier investigator, that the spiral, scalariform, reticulate, and 

 border-pitted types could be referred to a common origin. The 

 importance of these transitions was emphasized also by Pex- 

 hallow (7) in 1907 as affording valuable data on the ancestral 

 character of the bordered pit of the higher forms. In 191 9 Bailey 

 (1) argued that opposite pitting is formed by the breaking up of 

 bordered scalariforms, and that the alternate type was formed from 

 this by a "staggering" of the rows of pits. 



In this paper certain features of the primary wood of the 

 Cycads will be considered first. Fig. 1 is a longitudinal section of 

 the petiole of Cycas revoluta, showing the tangential walls of the 

 tracheids in the neighborhood of the protoxylem. The tracheid a 

 shows the characteristic spiral and scalariform structure of the 

 protoxylem. In transverse section (not figured) the scalariform 

 bars are seen to arch over the intervening spaces so as to form 

 very narrow borders. On the cell b the scalariforms are more 

 closely approximated, and through the slits may be seen shorter 

 pores, belonging to the adjacent wall of the next tracheid. The 

 tracheid c also shows this clearly. In the other two tracheids typi- 

 cal bordered pits are present. The type of scalariform from which 

 such bordered pits are formed is shown in fig. 2. It is a scalariform 

 similar to that formerly described, except that the borders are 

 wider. Fig. 3, another section from t a Cycas petiole, indicates 

 transitions in the formation of ordinary bordered pits from this 





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