150 BOTANICAL GAZETTE [ferruary 



THE EXTRAFASCICULAR CAMBIUM OF CERATOZAMIA 



CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 123 



(with plate vii) 



The anatomical features presented by the seedling of Ceratozamia 

 described in a previous paper (3) gave promise of such phylogenetic impor- 

 tance that the study has been continued upon older stems. The interest 

 centers mainly in the extrafascicular cambium — its origin, its distribution, 

 and its failure to differentiate xylem and phloem which could be clearly 

 recognized as such. In a careful examination of microtome sections of 

 over eighty seedlings, varying in age from a few months to two years, 

 only one small extrafascicular bundle was found. 



The origin of the concentric vascular zones of cycad stems puzzled the 

 early anatomists. Brongniart (1), failing to distinguish the phloem in 

 these zones, regarded them as the equivalent of the seasonal wood rings 

 of dicotyledons. Von Mohl (8) said that they were an aggregation of 

 bundles which passed out from the central cylinder and, running down- 

 ward in the cortex, grouped themselves in a ring. Lestibondois (4) saw 

 individual bundles in the cortex, but thought they foreshadowed the 

 breaking-up of the central stele, and so considered the cycads as a transi- 

 tion group from dicotyledons to monocotyledons. Mettenius, to whom 

 we are indebted for much of our knowledge of cycad anatomy, made no 

 attempt to explain the extra vascular zones. Constantin and Morot (2) 

 thought that the tissue arose from the pericycle. 



All the early research was confined to mature stems of Cycas and 

 Encephalartos. In 1890, Solms-Laubach (7) reported the absence of 



mexicana. In 1806 Worsdell (9) a 



„__ .wwrvvxsKVfVXA,* 111 1UUU Tl V/iVOA-'^^*- \^/ 



Macrozamia to the list of cycads in which these thickenings occur, and in 

 1898 (10) recorded their absence from the stem of Stangeria; in 1900 (I 1 ) 



he found them in the root of Bowenia spectabilis. His study of seedlings 



xtrafas- 



Worsdell 



cicular zones in mature stems arose as independent cortical cylii 



innermost 



~ ~**wj viic imicniiosi ones Deing coiiipuscvA v,* r - - 



tissue. By a later growth of the central cylinder they become apposed 

 to its periphery and flattened r a H,- a ii,r tw« ^a*, K™,.<rht to him and 



to its periphery and flattened radially, 

 to his readers a conviction 



to his readers a conviction of the truth contained in his earlier suggestion 

 hat the cycads are closely related to the Medullosae, which are poly*** 



like the ferns. 



_ . ; ~** ***o siuuy 01 L,ycas stamensts ana Mzm*>r— 

 Barten (5) j s an almost perfect demonstration of Worsdell's theory. 



phalarM 



