404 BOTANICAL GAZETTE [may 



vascular system of the lateral leaflets, and this is also frequently 

 the case when there are numerous lateral leaflets, as in pinnate 

 forms of Potentilla. 



On foliar evidence the connection of the stone fruits, whether 

 regarded as a tribe of the Rosaceae or as a separate family, with 

 the Potentilleae is quite direct. The nodal anatomy is the same 

 (Sinnott and Bailey 12) and the steps in leaf evolution appear 

 to be: (1) reduction of the lateral leaflets of a ternate or pinnate- 

 divided leaf to petiolar glands; and (2) splitting of persistent 

 adnate stipules from the petiole. In this series Prunus avium, 

 with an extensive development of glands, both in number and 

 size, or the apricot with a frequent reversion to leafy structures in 

 place of glands, would stand below Prunus americana with its 

 almost glandless petioles. Gregory (3) regarded the globose 

 gland as more primitive than the reniform, since when normally 

 glandless leaves produced glands, they were always of a globose 

 type. If, however, the trend is toward reduction of glands, the 

 glandless petiole would be the highest type, and the globose con- 

 dition transitional between it and the reniform. 



It has been customary to trace the connection of the drupes 

 with the more primitive Rosaceae through Spiraea (R ydberg i o) . 

 Considered on the basis of floral evidence alone, this seems a logical 



sequence, Spiraea 

 number of carpels 



in form of receptacle and 



Sinnott and 



Bailey (12) have shown, however, that Spiraea is exstipulate 

 and possesses a unilacunar node, while all species of Prunus have 



stipul 



fruits 



would appear that forms with 

 forms which lack them. The 

 :he true Rosaceae is probably 



more 



separating them as a distinct family than for considering them a 

 well defined and specialized tribe. 



Summary 



Examination of over 30,000 leaves belonging to 15 species and 

 interspecific hybrids of the plum shows that two glands typically 

 occur on the petiole, or less frequently on the leaf base. 



