Cells of the Medulla in the Laminariacece. 69 
the dilated parts of the elements almost up to the transverse wall 
or sieve plate. 
Fig. 13. Fig. 14. 
Fig. 13. L. digitata ; three of the longitudinally running element of the 
medulla. (Preserved in strong alcohol). 
Fig. 14. L. digitata-, part of a transverse section showing some of the 
invading cortical hyphae. (Preserved in Carnoy's fluid). 
Similar appearances have been noted from time to time in 
material examined at the Cambridge Botany School, and it seemed 
advisable to try to arrive at an understanding of their nature. The 
material from which Miss Saunders’ slide had been prepared was 
preserved in strong alcohol. Material of an old stipe of L. digitata 
preserved in Carnoy’s fluid was also examined, and showed the 
“thickenings” equally strikingly developed. Faint indications of 
similar “ thickenings” were found in the stipe of a young sporeling 
of L. saccliarina preserved in 70% alcohol,' where the walls of the 
medulla cells are as yet comparatively slightly mucilaginous and 
swollen. 2 The “ thickenings” always stain in the same way as the 
rest of the inner layers of the cell-wall; deep blue with methylene 
blue, faintly with Congo red, etc. 3 
It was found that the demonstration of these “ thickenings ” 
depended entirely on the methods followed in preserving, staining, 
mounting, etc. An old stipe of L. digitata in sea-water was kindly 
sent to me by Professor Yapp, and was examined while still fresh ; 
no such appearances were then present in the cell-walls. They 
could, however, be produced by drying, or by partially dehydrating 
the sections in alcohol. Material of L. digitata, L. saccliarina and 
Macrocystis preserved by killing and fixing entirely in aqueous 
solutions, without the use of alcohol, showed little or no trace of 
these “thickenings”; in sections obtained from the material pre- 
1 Ibid, p. 309, Stage 1. 
2 Oltmanns. “ Morphologie und Biologie der Algen,’’ Jena, 
1904, I., p. 446. 
3 Sykes, M. G., l.c., p. 312. 
