324 Sykes. — Anatomy and Histology of Macrocystis pyrij era and 
Fig. 28. A longitudinal section of a sieve-plate on which callus has begun to accumulate. 
(Thionin and London blue.) x 600. 
Fig. 29. A longitudinal section of a primary pith filament in which an aggregation of callus 
has been formed at the centre of the sieve-plate ; cf. Fig. 17. x 600. 
Fig. 30. An older element in which a large mass of callus has been deposited on the lower side 
of the sieve-plate, that is the side furthest from the apex, x 600. 
Fig. 31 is taken from a case in which a considerable amount of callus has accumulated on both 
sides of the sieve-plate and has also been deposited down the sides of the tube; cf. Fig. 23. 
(Stained Thionin and London blue.) x 600. 
Fig. 32. A cross connexion between two primary pith filaments; callus has been formed at the 
cross walls and is greater in amount at the wall which is nearer to the centre of the stem, x 750. 
PLATE XX. Laminaria saccharina (adult preserved i winter). 
Unless otherwise specified, the preparations from which the following figures are taken were 
stained by the Safranin method, followed by Aniline blue and London blue. 
Fig. 1. Surface view of the cross wall of a cell of the middle cortex. Five large primary pits, 
each divided into a number of secondary pits, are present. The ordinary wall is stained deep 
blue, the pit-closing membranes left white. (Stained Methylene blue.) X 600. 
Fig. 2. As Fig. 1, from the inner edge of the middle cortex, x 600. 
Fig. 3. Surface view of the cross wall of an outer cortical cell, showing the ends of the 
connecting-threads arranged in groups, each group corresponding to one of the primary pits in 
Figs. 1 and 2. x 600. 
Fig. 4. Surface view of the cross wall of an inner cortical cell just outside the secondary sieve-tube 
layer. The threads here are arranged in groups mostly confined to the pits, but a few are also seen 
in the central part of the wall, x 600, and drawing slightly enlarged. 
Fig. 5. Longitudinal section of a cell of the outer cortex, showing four pits in an end- wall, 
and connecting-threads as fine lines traversing the pit-closing membranes, x 600. 
Fig. 6. Two pits in a longitudinal wall of a middle cortical cell, showing the threads in longi- 
tudinal section, x 750. 
Fig. 7. A single pit on the lateral wall of an inner cortical cell, in longitudinal section, 
x 750, and drawing much enlarged. 
Fig. 8. Longitudinal section of a cell of the middle cortex passing through two pits in an 
end-wall, x 600. 
Fig. 9. Longitudinal section of a cell of the inner cortex, situated just outside the secondary 
sieve-tube layer. The end-wall is traversed by threads which are arranged in rather indefinite groups. 
Note very shallow pits, x 750, and drawing much enlarged. 
Fig. 10. Surface view of the cross wall of a young outer secondary sieve- tube, showing the ends 
of the threads arranged in a star-like pattern, x 600. 
Fig. 11. Surface view of the point of origin of a hypha from an outer secondary sieve-tube, x 600. 
Fig. 12. As Fig. 11. 
Fig. 1 3. Surface view of the point of origin of a hypha from an outer secondary sieve-tube, showing 
callus. x 600. 
Fig. 14. Surface view of the point of origin of a hypha after callus formation. 
Fig. 15. Longitudinal section of an outer secondary sieve- tube, showing the cross wall, 
partly in section and partly turned up so as to appear in surface view. The threads are arranged in 
small groups, x 600. 
Fig. 16 as Fig. 15. x 600. 
Fig. 1 7. Longitudinal section of an outer secondary sieve-tube situated the third from the periphery 
in a radial row. Callus has been formed, and each thread has its own callus-rod, which can be seen 
traversing the thickness of the plate, but the heads of the threads are fused together to form a mass. 
( a ) = origin of hypha. x 600. 
Figs. 18, 19, 20 are similar cases to Fig. 17. ( a ) = origin of hyphae at which callus formation 
has occurred, x 600. 
Fig. 21 is an unusual case in which a large accumulation of callus has taken place on one side 
of a sieve-plate in an outer secondary sieve-tube. The element from which this figure was taken 
was next to the medulla, x 600. 
