- (16, p. 171); I have traced their formation in the young stele of Acoris 
180 BOTANICAL GAZETTE 
leaf traces which arise in this region (fig. 16), but higher up retum 
to the stelar ring. It is probable that the anastomosing strands seen tf 
in Trillium, Zantedeschia, etc., are of the same nature. 
2. VANTIEGHEM (16, p. 172) has shown that in Acorus gramineus 
after a bundle has run for a distance in the medulla it divides, one 
part bending outward as a leaf trace, the other pursuing the medullary 
course, again dividing further on, and finally passing out to a leaf. 
The bundle marked 0 in jig. 2 is in process of division into a medullary 
bundle and a leaf trace. 
-  3- Medullary bundles are either absent or few in number in thi 
zomes, but become numerous as soon as the stem turns upward into 
the air; this is not altogether due to the greater development of leaves 
in the aerial part. 
It is probable that these strands have an important mechanical 
function, which may explain their paucity in rhizomes; they can 
hardly have arisen in consequence of a crowding out into the medulla 
of the too numerous vascular elements of the stelar ring, for they 
occur in stems whose meristeles do not form a complete ring, @ 
Smilacina stellata (fig. 19). . 
AMPHIVASAL BUNDLES. The mode of formation of these was 
observed by VANTIEGHEM in the mature stem of Acorus gramineus { 
calamus and Smilacina stellata. Starting with a simple collateral — 
bundle of the vascular ring it may be seen that the tracheids increase _ 
in number so as to give the xylem a U form and finally an 0 form. — 
Some strands never go any further than the U stage, and some that ; 
have become concentric lose the tracheids of their outer side. tt mae | 
Plain, then, that amphivasal bundles are derived from collateral wen A | 
and are simply a modification of the latter type. Since phylogeneti¢ 
significance has been attached to the concentric and mesarch bundles 
found in the petioles and peduncles of cycads, it has been thougy 
worth while to find in what parts of the plant in the Araceae ® 
Liliaceae the amphivasal bundles occur. The result of a somewhi cf 
extensive investigation of this point may be briefly stated as — | 
(1) only collateral strands are found in the lowest part of the stem" 
the seedling; (2) amphivasal strands are found in the older stem 
nearly every genus; (3) the floral axes show only collateral 
