aquilinum, with some Notes on Marsilia quadrifolia, &c. 585 
8. Connexions between sieve tubes and phloem parenchyma cells are 
frequent, but no callus was ever detected in connexion with them. 
9. From a limited examination, the impression was received that the 
development of the sieve tubes in Lygodium dichotomum and Marsilia 
quadrifolia resembles that in Pteridium aqUilinum. 
My thanks are due to Mrs. Thoday, to whom I am deeply indebted 
for her never-failing kindness and counsel, and for an initiation into histo- 
logical methods of research. 
Botany School, Cambridge, 1911. 
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EXPLANATION OF PLATES LIV AND LV. 
Illustrating Miss Hume’s paper on the Sieve Tubes of Pteridium aquilinum. 
\ 
PLATE LIV. 
Lenses used were Swift’s § ‘ apochromatic ’ objective, with 6, 8, and 12 Zeiss’s compensating 
oculars. Staining was with safranin and London blue except where otherwise stated. The blue 
colour in the figures represents callus. The figures throughout are of Pteridium aquilinum. 
Fig. 1. Longitudinal section of portion of sieve plate, abutting on parenchyma cells on the 
right of the figure, on another sieve tube on the left. Protoplasmic threads, showing a median node 
