AND THEIR BEARING ON STELAR THEORIES FOR THE FERNS. 
727 
in close contact with the wood (Ph.), and the pericycle is broad (Pr.). Text-fig. 5 
shows the general arrangement of tissues in median plane of a sporeling. Leaf- 
traces are lettered, root-traces are on the left, and levels referred to are numbered. 
Fig. 31 is from level I. At a slightly higher level a mass of parenchymatous cells 
is seen in the xylem. At the core of this parenchymatous pith sieve-tubes appear 
in the immediately succeeding sections. This inner phloem (Ph/, fig. 32) soon 
bulks largely in the pith, so that the parenchyma around it is reduced to a narrow 
selvage (S). This is the stelar state at II, a leaf-trace (a, text- 
fig. 5 ; L, fig. 32) is departing in the protostelic manner, and to- 
wards the upper side of the stele the xylem is thin and commonly 
interrupted. The number of leaf-traces which depart in the proto- 
stelic manner varies from plant to plant, but frequently a xylic 
gap follows the formation of the first or second trace after inner 
phloem is established. Through these xylic gaps inner and outer 
phloem may or may not be united. In text-fig. 5 their union is 
shown through the first xylic gap. There is no structural evidence 
of intrusion of outer phloem and parenchyma into the xylem- 
cylinder, and in these early stages there are no endodermal 
pockets. The medulla of thin-walled parenchyma and the sieve- 
tubes are then of intraxylic origin. As the stele is followed forward 
the arrangement of tissues just described is maintained. This is 
indicated in the upper portion of text-fig. 5, and inner and outer 
phloem are linked through the xylic gaps above leaf-traces b, c, 
and*d. The stelar structure during departure of trace c is shown 
in fig. 33. The outer phloem (Ph.) is a narrow band, the inner 
phloem is bulky (Ph/). They are united through the xylic gap 
before the arc of leaf-trace xylem and phloem (X) is free. As 
the stele expands by conical enlargement, the xylic gaps are suc- 
cessively longer. Through them pockets of increasing depth are formed within the 
stele. Thus the adult Lindsaya state is reached. 
It is thus apparent that in the ontogenetic progression from solid protostely to 
the adult Lindsaya structure, the formation of medulla and inner phloem involves 
neither cortical intrusion nor tissue -flow, but is the result of static intrastelar change 
by which also the pockets in the adult stele arise. The position taken on the 
structural facts is that in Lindsaya adiantifolia medulla and inner phloem are 
initiated in close succession at an early stage in the ontogeny. The phloem is from 
the first a bulky solid core around which the parenchymatous pith is a narrow 
selvage. The maintenance of this balance and distribution of stelar tissues with the 
addition of xylic gaps, endodermal pockets, and phloem-continuity through the gaps, 
gives the so-called Lindsaya type of adult stele. It is matter for no surprise that 
the Lindsaya state has been recorded for diverse genera, and figures in the early 
Text -fig. 5. 
