i9*o] DORSET &- WEISS— PETIOLAR GLANDS 405 



On the basis of vascular connections the glands on the petiole 

 or leaf base are of a different order of structure from those on the 

 leaf serrations. 



The stipules in the plum are morphologically integral with the 

 leaf base, and separate from the stem by a common abscission 

 layer. A portion of the node bearing the leaf and stipule scars 

 is subsequently shed in some species of Prunus as in other woody 

 genera; but the portion thus shed is not an additional foliar 

 element. 



On the basis of nodal anatomy and the presence of reduced 

 structures, the ancestral type of leaf in the plum is considered to 

 be a ternate lobed or divided simple leaf, the petiole glands repre- 

 senting the suppressed lateral members. In floral structure and 

 nodal anatomy Prunus and related genera form a logical series 

 with the Potentilleae, and should be considered as a specialized 

 tribe of the Rosaceae. 



Agricultural Experiment Station 

 University of Minnesota 



LITERATURE CITED 



1. Cook, O. F., Jointed leaves of Amygdalus. Jour. Wash. Acad. Sci. 

 2:218-220. 1912. 



2. Goebel, K., Organography of plants. Eng. trans, by Balfour, Oxford. 



J 905. pp. 359-376. 



3. Gregory, C. T., The taxonomic value and structure of the peach leaf 

 glands. N.Y. Agric. Exp. Sta. Bull. 365. pp. 183-222. figs. 2. 1915. 



4. Hedrick, U. P., et al., The plums of New York. Report N.Y. Agric. 

 Exp. Sta. 1910, vol. 2. 1910. 



5- , The cherries of New York. Report N.Y. Agric. Exp. Sta. 1914, 



vol. 2. 1914. 

 6. , The peaches of New York. Report N.Y. Agric. Exp. Sta. 191 6, 



vol. 2. 1916. 



7. Lewis, F. T., The development of pinnate leaves. Amer. Nat. 41:431- 



44i. figs. 4- i9°7- 



8. — 9 A further study of leaf development. Amer. Nat. 41:701-709. 



figs. 15. 1907- 



9. Lloyd, F. E., Abscission in Mirabilis Jalapa. Bot. Gaz. 61:213-230. 



pi. 1. 1916. 

 o. Rydberg, P. A., Monograph of the North American Potentilleae. Mem. 



Dept. Bot. Columbia University. 



