324 Gwy nne- Vaughan. — On Polystely 
far the greater portion of the ring of desmogen is formed 
by the leaf-trace that has latest entered it, a fact completely 
in accordance with the manner in which the leaf-traces regu- 
late the arrangement of the vascular system in the fully 
differentiated stem. 
The greater part of this paper was prepared at the Royal 
Gardens, Kew, and I desire particularly to express my 
gratitude to Dr. Scott, the Honorary Keeper of the Jodrell 
Laboratory, for the interest he took in my work, and to thank 
him for the valuable advice I received from him at almost 
every point of the investigation. I have also to thank the 
Staff of the Gardens for the supply of material which they 
placed at my disposal. 
EXPLANATION OF FIGURES IN PLATE XIV. 
Illustrating Mr. Gwynne-Vaughan’s paper on Polystely in the Genus Primula . 
Note. — Figs. 1, 5, and 6 only are to be regarded as accurate drawings. The 
insertion of the leaf-traces and adventitious roots, and also the presence of the 
radiciferous network, cause so much confusion among the vascular elements that 
I was obliged, for the sake of clearness, to make the other figures somewhat 
diagrammatic, although in every case I follow the actual sections as closely 
as possible. 
Abbreviations : m. medulla ; x. xylem ; ph. phloem ; p. pericycle ; e. external 
endodermis ; i. internal endodermis ; c. cortical tissue ; /. t. leaf-trace ; /. g. leaf- 
gap ; s. a stele of the stem. 
Fig. 1. Primula japonica\ portion of transverse section of an imperfect stele ; 
r. the elements of the radiciferous network ; ext. b. external bundles. The 
internal bundles are completely absent, x 130. 
Figs. 2, 3, 4. Primula involucrata ; portion of transverse section of the stem, 
showing a leaf-trace entering between two perfect stem-steles. X40. In Fig. 2 
the leaf-trace is seen approaching the steles ; in Fig. 3 it has become fused with 
both of them. Fig. 4 shows the imperfect stele thus produced, which has no 
internal bundles in its median region. 
Fig. 5. Primula denticulata ; transverse section of the median leaf-trace in the 
petiole. The stele is not yet perfect, but the vascular ring is open towards 
the upper surface, x 90. 
