I909 j BRIEFER ARTICLES 151 



Mv work upon Ceratozamia will come as cumulative evidence. Solms's 

 statement concerning the absence of extrafascicular zones is correct as 

 far as the seedling is concerned; but the presence of extrafascicular cam- 



urn 



horizontal 



u 



relation to the central cylinder. In the study of seedlings described in the 

 previous paper I was unable to do this on account of the disturbances 

 caused by mucilage ducts, which are large, abundant, and irregular in 

 distribution. In the study of older stems I have been more fortunate. 

 Four-year-old seedlings have in the hypocotyl clearly distinguishable 

 rings or cylinders of cambium. The cylinders are arranged in several 

 series. Those of the innermost series, though decidedly flattened, are 

 the most distinct. 



Fig. 1 represents diagrammatically a section of the hypocotyl slightly 

 below the exit of the cotyledonary traces. The innermost cylinders 

 («, b, s) arise in the pericycle near the transition region and are of primary 

 origin. They extend well up in the stem, though pushed outward by the 



hmW.1 -^J-j The other rfngs appear later> ^ would 



**m mat the single bundle described in the previous paper (3 



was differentiated from one of the outermost series of cylinders. 



F k- 2 is a detail of the inner portion of half the section represented in 



H- 1- One large cambial ring (a) is represented, and ends of two others 



(* and s). Several small rings (e, r) suggest how concentric bundles might 

 arise. 



The cause of the flattening is manifestly the enlargement of the central 

 cylinder and the consequent pressure upon the inner side of the cortical 

 cylinders (a, b, s). The final result is a central cylinder surrounded by 

 ^eral more or less imperfect zones of cambium cells. The xylem and 

 PWoem which these cells might produce would be oriented differently; 



* xylem on the centripetal side of the zone would be differentiated toward 

 m * pen P he ry and the phloem toward the center of the stem. But in 

 ^any cases, the inner cambium of each zone would cease to function, and 



* s ould then have successive zones of alternating xylem and phloem all 

 Wo . normal orientation. Occasionally a bit of the elongated cylinder 

 ^ be disconnected, the cambium would round out, the growth of 

 All th W0UW diminate the P ith > and a concentric bundle would result. 

 j ike ** e cond itions are found in the Medullosae, from the distinct fern- 

 % Jv Stdy in M ^ullosa Solmsii and M. anglica to the condition of 



* * fl to, which closely resembles Cycas revoluta. 



»ell f? 1 0t yet examin ed mature stems of plants of this genus. 

 W has confirmed Solms-Laubach's statement that the e: 



Wors- 



extrafas- 



