august] BOTANICAL GAZETTE 124 



Grateful acknowledgment is made of the helpful criticism and 

 advice given by Professors John M. Coulter, Charles J. Cham- 

 berlain, and W. J. G. Land during the progress of the investi- 

 gation. The writer is also greatly indebted to Dr. Chamberlain 

 for the very generous supply of material. 



Goucher College 

 Baltimore, Md. 



LITERATURE CITED 



1. Chamberlain, C. J., Dioon spinulosnm. Bot. Gaz. 48:401-413. 1909. 



2. , The adult cycad trunk. Bot. Gaz. 52:81-104. 1911. 



3. Dorety, Sister Helen A., The seedling of Ceratozamia. Bot. Gaz. 



46:203-215. 1908. 

 4. -, Embryo and seedling of Dioon spinulosum. Bot. Gaz. 67: 251-256. 



1919. 



5. Dyer, Sir W. T. Thistleton, Biologia Centralia Americana. Botany 

 3:190. 1885. 



6. Eichler, A. W., Ein neues Dioon. Gar tenflora 2:411. 1883. 



7. Karsten, H., Organographische Betrachtungen der Zamia muricata 

 Willd. Abh. Berlin Akad. 193-219. 1856. 



8. Langdon, LaDema M., Sectioning hard woody tissues. Bot. Gaz. 

 70:82-84. 1920. 



9. Matte, Henri, Recherches sur l'appareil libero-ligneux des Cycadacees. 

 Caen. 1904. 



10. Mettenius, A., Beitriige zur Anatomie der Cycadeen. Abh. Konigl. 

 Sachs. Gesells. Wiss. 7:565-608. 186 1. 



11. Thiessen, R., The vascular anatomy of the seedling of Dioon edule. 

 Bot. Gaz. 46:357-380. 1908. 



12. Worsdell, W. C, The anatomy of the stem of Macrozamia compared 

 with that of other genera of Cycadeae. Ann. Botany 10:601-620. 1896. 



13. ■ — , The comparative anatomy of certain species of Encephalartos 



Lehm. Trans. Linn. Soc. 24:445-459. 1899. 



EXPLANATION OF PLATES XV-XVII 



All the drawings were made with the aid of a camera lucida, except figs. 

 8, 9, 10, n, which are diagrams showing origin and distribution of foliar 

 vascular strands, as traced from cleared material, supplemented, where detail 

 in connection was required, by serial sections; figs. 1-3 and 12 are in the text. 



PLATE xv 



Fig. 4. — Mature wood: radial longitudinal section of large foliar ray, 

 showing organization of leaf trace and structure of scalariform tracheids of 

 trace: b, bulbous bases of tracheids; c, calcium oxalate crystals; X90. 



