COMPARATIVE ANATOMY OF THE CYCADACE E. 441 
youngest part of the root of the young seedling appears to have 
four protoxylem groups. 
We thus see that it is as part of the earliest-formed tissues of 
the seedling that the anomalous strands arise, for they gradually 
dwindle and disappear both in passing upward into the plumular 
stem and downward into the root. 
The tracheides in the plumular stem, cotyledons, and scale- 
leaves have scalariform thickenings on their walls, which, 
however, merge into slit-like pits and close reticulatious. 
Older Seedlings. 
Two other seedlings of this plant came to my hand, both of 
which are very much older than the last two described, and have 
already undergone a considerable amount of secondary thickening ; 
they bear two or three foliage-leaves. The chief features in their 
structure, to be eularged upon below, are: the extrafascicular 
collateral zones of secondary thickening outside the central 
cylinder, the secondary concentric strands and the obliquely out- 
going strands in the cortex, and the occurrence of centripetal xylem 
in some of the leaf-traces in the stem. 
In the hypocotyl and the lowest part of the stem the central 
cylinder is surrounded by a conspicuous irregular band of vascular 
tissue, consisting of xylem and phloem in the normal position, 
which in places is broken up into small semi-concentric strands. 
In one of the plants, an extra strand, but very weak and incon- 
spicuous, and with inverted orientation of parts, occurs between 
the central cylinder and the first extrafascicular strand (cf. Ma- 
erozamia Fraseri, Miq.) *. Lower down iu the hypocotyl these 
extrafascicular strands break up into concentric structures, several 
in number and of different sizes, which still lower down die out. 
Passing in the opposite direction upward through the stem, the 
outer strands become reduced and isolated and finally fuse with 
the central cylinder. Some, however, appear to end blindly in 
the cortex. 
These strands are all secondary in origin, and doubtless re- 
Present a more advanced stage of the small concentric strands 
described in the root of the young seedlings. 
In the hypocotyl broad strands are seen passing out obliquely 
from the central cylinder, sume of which arise opposite a proto- 
* Worsdell: * On the Anatomy of Macrozamia, as compared with that of 
other Genera of the Cycadez," Ann. Bot. vol. x. 1896, pp. 610-612. 
