CYCADALES 97 



bundles in the pith. In 1841 Miquel (3) published his monograph 

 of the group, and included the anatomy of several genera. In 1861 

 Mettenius (4) published the account of cycadean stems which long 

 remained the chief source of information concerning them, including 

 Cycas, Encephalartos, Dioon, and Zamia, and discovering in the last 

 two genera none of the secondary cortical bundles characteristic 

 of the first two. In 1885 Constantin and Morot (14) investigated 

 Cycas siamensis, and stated that the cortical cambium has its origin 

 in tiie pericycle. In 1890 Solms-Laubach (16) traced the vascular 

 bundles of Stangeria from the peduncles to the stem cylinder, and 



Fig. 74. — Cycas revoluta: transverse section of stem, showing pith, two concentric 

 zones of xylem, cortex, and armor of leaf bases; one-half natural size. — After Brong- 

 NIART (i). 



found no evidence of cortical bundles. In 1891 Strasbueger (17) 

 brought together the knowledge of stem anatomy with reference to 

 Cycas, but did not include other genera. Then came the work of 

 Worsdell on Macrozamia (20) and Bowenia (30), and that of Scott 

 (23) on the peduncles of cycads. Since 1900 the vascular anatomy 

 of cycads has been investigated with increased intensity, including 

 every region of the body, and especially the seedling. 



The primary cambium may be short-Kved, as in Cycas; or persist- 

 ent, as in Dioon; but, in any case, the growth of secondary xylem is 

 very slow. There are no annual rings, although growth rings, resem- 

 bling them but not corresponding to seasons, occur in Dioon. In 

 case the cambium is short-lived, a succession of secondary cambiums 

 in the cortex produce cortical cylinders (fig. 74). The first cortical 



