134 Seward and Gowan .— The Maidenhair 
v. Roots. 
Van Tieghem 1 and other writers have described some of 
the anatomical features of the roots of Ginkgo. Fig. 51, PI. X, 
represents a section of a young primary root; the piliferous 
layer produces long unicellular hairs, of which traces can be 
seen in the photograph ; this is succeeded by one or two layers 
of rectangular suberized cells and four layers of cortical 
elements; next to this tissue there are two layers, or some¬ 
times only one layer, of cells with strong thickening bands on 
their radial walls (Fig. 51, e). The pericycle is made up of 
seven to eight layers of almost spherical cells, but opposite the 
two xylem plates this tissue is narrower. A radial longitu¬ 
dinal section through the place of origin of a lateral root 
demonstrates the existence of several short tracheids with 
bordered pits between the spiral protoxylem and the tracheids 
of the lateral root. The spiral tracheids of the protoxylem 
are succeeded by elements with reticulate pitting, and beyond 
which there are tracheids with large transversely elongated 
simple pits which gradually pass into the elements with 
smaller bordered pits 2 . 
In the seedling root the stele is at first diarch ; but at 
a higher level the splitting of first one and then the other 
xylem strand produces a tetrarch structure ; at a still higher 
level a fifth protoxylem group appears, and afterwards a sixth 
is found on the opposite side of the stele, thus producing an 
hexagonal arrangement (PL X, Fig. 55). Scattered xylem- 
elements (metaxylem 3 ) appear in the pith, and these may be 
abundant enough to entirely replace the central conjunctive 
tissue. In the hypocotyl the cambium forms rows of centri¬ 
fugal xylem except at the two ends of the stele, the latter 
gradually increases in diameter, and from the two ends of the 
longer axis of the xylem-ring, groups of tracheids pass out as 
the cotyledon-traces ; the stele then becomes closed again, 
1 Van Tieghem (70), p. 195 ; (’87), p. 105 ; also Van Tieghem and Douliot 
(’ 88 ), p. 349 , and Strasburger (72), p. 350 . 
2 Cf. Dippel (’62), PI. VI, Fig. 1 . 
3 Van Tieghem (’87), p. 105 . 
