Young Plant of Macrozamia Fraseri. 
573 
derived from the arms of the irregular 12, enter each pinna ; these soon 
dichotomize, and there are four parallel bundles throughout the greater 
portion of its length ; near the apex, these are again reduced to two 
by fusion. 
(2) The stem apex and leaf-traces. The youngest leaves are fleshy, 
hooded structures which overtop the stem. At the immediate apex no 
distinction of layers can be made out ; but immediately below there is 
a solid, central meristematic dome, occupying the centre of the stem, from 
which the leaf-traces arise. The traces themselves are not distinguishable 
within the cylinder at this level, but are recognizable as they leave it. 
PL 
Text-fig. 5. a. Transverse section of plant just above stem apex, showing bases of five 
youngest foliage leaves. B. Transverse section of same plant taken just below stem apex, showing 
vascular bundles of young foliage leaves in stem. ® = bundles of leaf a (shaded) ; @ = bundles of 
leaf b (hatched) ; O = bundles of leaf c (unshaded) ; a, b, c, d, e = first five 'foliage leaves in order of 
development ; a (g) = girdling traces of leaf a ; b (g) = girdling traces of lenf b, and so on ; PI. = 
plerome. N.B. Peripheral portions of sections, showing traces of older leaves, are omitted in each 
case for the sake of clearness, x 3. 
Each leaf receives 4-6 strands, which arise in the same horizontal plane at 
points widely distributed round the central cylinder (Text-fig. 5). Of 
these strands, those which originate in that half of the central cylinder 
adjacent to the leaf pursue a radial and slightly ascending course into the 
middle (midrib) region of that leaf, while those which arise from that 
portion of the cylinder which is removed by 180° from the leaf midrib 
swing round right and left from their point of origin, pursuing tangential 
and slightly ascending courses into the marginal regions of the leaf 
(Text-fig. 5. Cf. A and B). 
The first system, which may be designated the midrib system, represents 
the £ direct ’ strands of the mature leaf. The second, marginal system 
constitutes the ‘ girdling ’ strands, the tangential portions of their course 
P p 
