Transition from Stem to Root in Palm Seedlings. 57 
therefore, to deal with a plant in which the plumule has broken 
through the cotyledonary sheath, and grown out to some little 
length. A seedling at this stage is shown in Text-fig. 4. The primary 
Fig. 4. Phoenix dactylifera. 
root in such a seedling possesses about twelve xylem groups— 
the number varying from seedling to seedling. These xylem groups 
are for the most part independent of one another, and alternate 
with the phloem groups. The V-formation so often found in the 
large adventitious roots of mature palms is however occasionally 
present here also, the large metaxylem vessels of two bundles being 
approximated in such a manner that the two xylem groups form 
a V—the end of each limb being occupied by a protoxylem group, 
(Fig. 5 i.) At this stage the protoxylem consists of a few—three 
to six only—annular and spiral elements. As we follow the root 
upwards the metaxylem portions of the bundles are seen to be 
more and more united, and at the stage shown in Fig. 5 ii., there 
are four groups of metaxylem with respectively five, four, three 
and two protoxylem groups placed peripherally. At the same time 
the place of the large radially arranged metaxylem vessels is 
occupied by tracheids and vessels of a different character, 
resembling those of the stem-bundles. Following the root still 
further upwards, a gradual “ splaying out ” of the protoxylem 
groups is seen, and in many cases ground-parenchyma appears 
between the exarch protoxylem vessels and the metaxylem groups, 
(Fig. 5 iii.) The metaxylem elements just referred to as re¬ 
sembling those of the stem-bundles now give place to smaller 
elements, recalling in appearance the protoxylem of the typical 
root but having reticulately thickened walls. 
