480 Pearson. — Anatomy of the Seedling of 
which is made up of sieve-tubes, some parenchymatous tissue, 
and small groups of long, very thick-walled, fibrous elements 
(Fig. 7), which, as Worsdell 1 has pointed out in the case 
of the stem of Macrozamia , must have an important function 
in an organ so largely composed of parenchymatous tissue. 
A few cells filled with cluster-crystals of calcium oxalate are 
also found in the secondary phloem. 
Opposite each primary xylem-group the cambium produces 
no secondary phloem, but a wide medullary ray (Fig. 6, 
m. r.). The medullary rays, as well as the pith and pericycle, 
afterwards increase rapidly in extent by primary cell- 
division, and consequently the arrangement of the secondary 
tissues, which is at first so regular as to be almost 
diagrammatic, becomes considerably disturbed. 
No indications of growth in thickness of an anomalous 
character were observed. 
The lateral subterranean roots arise in a normal manner 
from the main root, and are similar to it in structure, though 
the number of primary xylem-groups is commonly fewer 
than in the main root. Among the lateral roots a diarch 
or triarch structure is usually found. 
The Apogeotropic Roots. 
These roots spring from the upper portion of the main 
root, the first of them appearing a short distance below the 
origin of the cotyledons. Later ones are produced at points 
lower down, but apparently not in strictly acropetal succession. 
The term ‘ apogeotropic 5 is strictly correct as applied to 
these roots, for as soon as they emerge from the main root 
they grow vertically upwards. When full-grown, the apo- 
geotropic root is from 2 to 4 cms. in length, and consists of 
a cylindrical stalk which bears above the surface of the ground 
a much-branched ‘coralloid’ head (Fig. 1, a. g., and Fig. 2). 
A remarkable feature of these roots is that their branching 
is of an exogenous type. At the apex is a merismatic 
1 Worsdell, The Anatomy of the Stem of Macrozamia compared with that of 
other genera of Cycadeae, Annals of Botany, Vol. x, 1896, p. 608. 
