﻿62 



VEGETATIVE FEATURES. 



the three bundles in the lower angle of the leaf base, while each of the lateral 

 branches dichotomizes twice in such a manner that the fourth bundle formed swings 

 from beneath into the upper angle of the leaf base, there to form with its mate and 

 the other lateral and median bundles a regular peripheral distribution. 



An interpretation of the cyeadeoidean leaf-base bundle patterns may best be 

 made if it first be recalled that the petiolar bundles form a closed or simple circular 

 pattern in Stangeria and Bowenia, and are irregularly distributed in Enccplial- 

 artos ; while in most, if not all the other genera of existing cycads the pattern 

 of an inverted omega is finally assumed {cf. figs. 32 and 33). Normally the xylem 

 is interior or inverted, using this word in the sense of inturned, while the phloem 

 is everted or out-turned. But in Enccphalartos (fig. 32, No. 5), excepting the 

 peripheral layer of bundles with inverted xylem, extending around most of the 

 under side of the petioles, the numerous bundles have no distinct xylem orienta- 

 tion, and the grouping is a mixed one, presumably obscuring an omega pattern. 

 Moreover, the simple or Bowenia form develops into the omega pattern by simply 

 opening out above. The two outer branches then give rise to the pinnule supply 

 by simply spreading upward and outward till their xylem comes to be superior. 



Fig. 32. — Typical bundle patterns and features of the petioles and petiole bases of existing cycads. 



I . Bowenia spectabilis. X IJ^. 



2. Zamia floridana. Leaf base near cortical insertion showing the emergence of the right-hand girdle leaf trace from the cortex. 



3. Zamia Roezlii, showing a bundle trace as given off to a pinnule. 



4. Encephalartos (?l cycadifolius. X 2. 



5. ELncephalartos Vroomi. X 2. 



6. Cycas celebica. ■ \.. Basal portion of petiole, and three serial transverse sections of the same, showing origin of inverted 



omega bundle pattern from a simpler form. In the lower section 38 bundles are cut, these increasing to 42 in the middle 

 section, and this number continuing the same in the upper section. 



In the Cycadeoideae the necessity for comparing the leaf base rather than the 

 petiolar pattern in many cases prevents a close comparison ; but the data at hand 

 indicate, as has just been noted, a more fern-like closed pattern to be the character- 

 istic one, with a pinnular bundle supply arising from the tipper sides of the system, 

 as left by a depression of the middle upper bundles into a deep U-shaped valley, 

 instead of a parting of the series as in the omega form. There is also, as has been 

 seen in C. Jenneyana, C. iiigcns, and C. gigantca, a mixed distribution, much like 

 that of Encephalartos ; while in C. nigra the two additional groups of bundles cir- 

 cularly arranged, or else two single brokenly-cyliudric bundles in the upper U-like 



