8o 
Birbal Salmi. 
ribbon-like strands composing the reticulate stele. 
I wish to express my hearty thanks to Professor Seward for 
his kind interest in the work and also for revising the manuscript 
of this paper. 
Summary. 
The strand of the branch-stolon penetrates the base of the 
tuber as a solid protostele for a few millimetres (Pig. 1, A), but 
rapidly expands in a funnel-like manner, acquiring, in succession, 
internal phloem, pericycle, endodermis and ground-tissue (Figs. 2 
and 3). Sooner or later the funnel-like stele breaks up, while at 
the same time expanding enormously, into a hollow net-work of 
tangentially flattened ribbon-like strands (each concentric in 
structure), enclosing gaps of irregular shape and size. These 
strands converge again into a single protostelic strand. The latter 
as a rule ends in the apical mamelon, which contains the apical cell; 
but when the mamelon is developed into a stolon the strand is 
continued into the latter. 
Root-strands arise promiscuously from this reticulate stele. 
The process of fusion of strands at the apex is similar to the 
process of stelar disintegration at the base, the relative duration of 
the various stages in the transition depending upon the rapidity 
with which the tuber tapers towards its ends. This relation is 
inverse. 
Attention is drawn to the superficial but close similarity of 
some of the stages in the transition to those passed through by 
many fern-rhizomes in their development from the protostelic to 
the dictyostelic condition. There being no sign even of reduced 
leaves on the tuber, the gaps cannot be traced to any influence 
from leaf-traces, which in normal fern-rhizomes have justifiably 
been held to be the dominating factor in the evolution of the 
cauline stele (Boodle, Gwynne-Vaughan, Tansley). It is suggested 
that the necessity of adequately supplying food to all parts of the 
tuber has “called forth” in the originally solid stele a dilatation 
great enough to transform it into a hollow net-work ; this dilatation 
being similar to that “ necessitated,” according to Tansley, by the 
increase in the span of the C-shaped leaf-trace, to the attachment 
of which on an originally solid stele he traces the root-cause of the 
departure towards solenostely. 
The reticulate stele of the tubers of Nephrolepis is unique 
because all the gaps in it are what have technically been called 
“ perforations.” 
The Botany School, Cambridge, 
March , 1916. 
