﻿EXISTING AND FuSSU. CYCADS COMPARED. 



199 



leaf-base bundle. The relatively small amount of woody fiber as compared with the 

 parenchyma of the xylem zone itself is a striking feature in the tuberous trunks of 

 the Zamia type, quite in contrast with the solidly developed xylem and phloem 

 regions often noted in the Cycadeoidese. But to be complete and final, all such 

 comparisons would have to be based 011 wood from the same serial portions of 

 trunks of about the same age or development. 



(6) In Cvois, Afacrosamza, Encepkalartos, and Bowenia the xylem zone does 

 not remain single as just described, but is anomalously repeated a number of times 

 in the cortex, although with less and less distinctness. Roughly speaking, this is 



a character of the cycads of columnar 



form, but, as we see, it is present in the 



low-growing Bowenia, while among 



^M^BSS the more cylindrical types Dion and 



■%,,JI ";ETrf\ D Ceratozamia have but a single vascular 



sW ) zone. The polyxylic trunk is like the 



\\-m monoxylic form up to a certain age 



^iqjBSt::;- I and size ; then lateral but not apical 



growth ceases in the primary cylinder 



of anastomosing bundles, and there are 



)—c successively developed, outside and 



" „ hii „ //' *-/-">-. I concentric to it, from one to as many 



V A l» t ° */,.' I o . .7 "" 1 as a dozen cortical cambiums of 



' 'i$^kdikiiyk$$MJm ' ~~-~-~- : ^~ a diminishing power, from which arise 



. a - the additional or anomalous vascular 



zones, these being strongest near the 



base of the trunk, weaker and weaker 



" from within outwards, and of less and 



\ less strength toward their growing 



■JM- I apices. 



■i\°i'7 - I In transverse sections from the 



\*J/ J lower portion of well-grown polyxylic 



Fig. I I I .-Macrozamia Fraseri. Transverse sec.ion of trunk. stelI1S tllere is See » t0 abut # immediately 



X %• (From Worsdell.) on the normal vascular ring a second 



P. Periderm in successively formed layers; w. wall of one of the leaf j J t liear ] y or equa l \ n W idtll to 



bases; 1 . leat base; c, cortex; g, girdle leaf traces; a , isolated bundle o T. J ± 



of a third anomalous wood zone: a', second anomalous zone; a. first t ] Je flj-gf an( \ aS 111 fig. Ill, a third, aild 

 anomalous wood zone; n, normal wood (xylem dark, phloem light); 



m. medulla; m'. medullary bundle. yet others of less and less size may 



follow. The xylem of the second ring closely follows the first-formed phloem of 

 the first, and so on, the structure and orientation of the consecutive parts being in 

 general the same, although the segments of these several successive rings lie less 

 and less evenly radial to each other. Occasionally also a wedge of the secondary 

 wood is pushed out of line and lies embedded in a large pith ray so nearly between 

 two segments of the next inner ring, whether this be secondary or primary, that it 

 is not always at first easy to tell to which ring a given bundle segment belongs ; 

 and this kind of irregularity increases with the diminution in the size of the 

 segments, so that there is less strength and less definition in the successive rings 



