iQ2o] DORSEY &• WEISS— PETIOLAR GLANDS 399 



on the leaf base, as of the same structure but of different rank 

 from those borne on the serrations. This is in keeping with the 

 evidence presented in the statistical analysis in which the number 

 two figured so prominently, that is, two glands on the petiole and 

 none on the leaf base, or one in either position, or less frequently, 

 two on the leaf base. The points emphasized are of significance 

 from the standpoint of phylogeny, and will be given greater em- 

 phasis from that standpoint. 



Phylogeny of leaf as indicated by glands, vascular system, 



stipules, and abscission layers 



There are structures other than the glands whch are significant 

 from the standpoint of the ancestral type of leaf in Prunus and 

 related genera. Cook (i) called attention to a joint in the leaves 



Amv 



the 



separate abscission from that of the leaf proper. This "basal sec- 

 tion" is regarded as belonging to the leaf on the basis of the 

 attachment of the stipules to it, although the stipules themselves 

 absciss early, and hence "the persistence of the base of the leaf" 

 has been overlooked. Goebel (2) characterizes stipules as "ap- 

 pendages arising at the insertion of a leaf, attached either wholly 



the 



SlNNOTT 



(12) regard the stipules as arising through the stimulus of the 

 growth of the lateral leaf trace, and although they are morphologi- 

 cally integral parts of the leaf, in some exstipulate families having 

 trilacunar nodes, they are represented by mere swellings opposite 

 the leaf trace. In some stipulate genera with opposite leaves, as 

 Viburnum, the stipules arise midway between the insertion of the 

 petioles, apparently directly from the stem. Cook also states that 

 in Texas this basal section in the peach may remain alive for a 

 year or two and then wither away; while in Maryland it lives 



leaving 



green scar. 



In most of the plums studied in this investigation, this structure 



may 



with 



