the Sieve-tubes in Laminar ieae . 
ii 1 
Fig. 13. Macrocystis pyrifera. Complex arrangement of branched trumpet- 
hyphae. (x 750.) 
Fig. 14. Macrocystis pyrifera. Longitudinal radial section of the true sieve- 
tubes, showing three sieve-plates in three different planes. S. the sieve-plates, 
all of which are callous. The callus is drawn in red, /. lumen of sieve-tube 
between the wall and the contracted contents, p. ( x 300.) 
Figs. 15, 16. Macrocystis pyrifera. Much magnified views of fully developed 
callus-plates on the sieve-plates. 15 shows still a number of depressions and 
striae which represent the perforations so far as they survive; in 16 they are 
no longer visible. ( x 450.) 
Fig. 17. Macrocystis planicaulis. Showing a very typical adult callus-plate 
in this species, (x 550.) 
Fig. 18. Macrocystis Orbignyana. Showing a callus-plate with curious irregular 
appendage, which might point to the callus being deposited by the protoplasm, 
(x 400.) 
Fig. 19. Macrocystis Orbignyana. Early stage in the development of callus 
in a true sieve-tube. It arises over the cellulose-framework of the sieve-plate. 
The perforations are still quite open. The protoplasm is not drawn in. (x 570.) 
Fig. 20. Nereocystis Liitkeana. Showing a true sieve-tube from a young 
specimen before the appearance of callus. ( x 500.) 
