272 BOTANICAL GAZETTE [APRIL 
EXPLANATION OF PLATE XVII 
Fic. 1.—Petiolar bundle of Cycas revoluta, showing the typical cycadean 
condition, with primary-and secondary phloem, primary centripetal xylem, 
and secondary centrifugal xylem; 150. 
1G. 2.—Typical petiolar bundle of Encephalartos La showing com- 
plete absence of centrifugal wood; - X 250. 
Fic. 3.—Petiolar system of Zamia Loddegesii, showing the small amount 
of stclttigal wood and its radia] arrangement. : 
Fic. 4.—Longitudinal section of a bundle of Cycas revoluta, with centrif- 
ugal wood on the left and centripetal wood on the right; the protoxylem 1s 
clearly in seriation with the latter; X 100. 
Fic. 5.—Bundle from the base of the petiole of Zamia macrophylla, show- 
ing the protoxylem attached to both centrifugal and centripetal wood; 120. 
Fic. 6.—Leaf trace of Lyginodendron at its separation from the stele, 
showing the diarch condition; oS 
