730 
DR JOHN M'LEAN THOMPSON ON NEW STELAR FACTS, 
from protostely to solenostely are due to a static change of quality of procambial 
cells as the growing point advanced. 
Acrostichum aureum * 
In Loxsoma the internodes are long, and solenostely is delayed until many 
leaves have been formed. But in many ferns with upright stocks the internodes 
are short, and certain ontogenetic steps are apt to be abbre- 
viated or even omitted. This may be illustrated by Acro- 
stichum aureum , a plant of Pterid affinity. Text-fig. 9 shows 
the arrangement of stelar tissues in the juvenile axis of a 
sturdy plant. The stage of solid protostely is brief (I), only 
one leaf-trace departing in the protostelic manner before 
medullation occurs (a). As the stele expands upwards, a 
medullated stage with a xylic gap is reached (II). Higher up 
a core of phloem appears in the pith (Ph.). At first it is solid, 
but later is tubular and encloses parenchymatous pith (M). 
In the latter an inner endodermis is initiated, as in Gleichenia 
pectinata, Loxsoma Cunninghamii, and others considered (e). 
It is held to be potentially the base of the pocket which opens 
into the first leaf-gap, but is not maintained and dies out as 
a spindle when followed upwards. Higher up an inner endo- 
dermis is permanently established, beginning as a pocket 
opening on the one hand into the first leaf-gap (g), and on the 
other being continued as the inner endodermis of a typical 
solenostele (III). Thus in the ontogeny of Acrostichum aureum 
the Lindsaya stage is brief, and enclodermal pocketing is 
omitted from the early solenoxylic stages. That its omission 
goes hand in hand with the early attainment of solenostely 
is the view here adopted. In some of the specimens examined 
solenostely arises even earlier in the ontogeny than in the 
example described. In them isolated spindles of inner endo- 
dermis do not occur, but solenostely is secured with the 
first formation of inner endodermis within the pith. The 
ontogenetic condensation thus shown for Acrostichum aureum 
appears also in Cheilanthes, and in Pteridium aquilinum (33), 
(48), and Psesia podophylia (ll), and may be expected to figure generally for 
plants of Pterid affinity. 
There is already a body of ontogenetic facts which are known for a number of 
genera,, The early stages of the sporeling of Anemia phyllitides have been 
described by Boodle (3), but the actual transition to solenostely was not traced. 
* The materials on which this study was made were kindly provided hy Professor I. B. Balfour, F.R.S. 
