aquilinum , with some Notes on Mar si Ha quadrifolia , &c. 587 
completely dissolved. The paired granules of the middle slime string have sunk in unequally. The 
paired granules of the bottom one are connected by a thick slime string and the median nodule is 
still visible. x 1,000. 
Fig. 21. A longitudinal section showing four slime strings. The granules have sunk more 
deeply in and almost abut upon one another, x 1,000. 
Fig 22. Longitudinal section of a single slime string. The granules connected by a short thick 
slime string, x 1,000. 
Fig. 23. Longitudinal section of a single slime string. Two granules in contact across the 
middle lamella, x 1,000. 
Fig. 24. Longitudinal section of a single slime string. The granule on one side has sunk in 
almost to the middle lamella. The granule of the other side has become dislodged in cutting and 
is lying near. The secondary pit formed by the solution of the callus and from which the granule 
has been dislo,dged is visible. The sieve plate is one containing only the single slime string 
illustrated, and the thickened portions of the wall limiting the sieve plate are visible behind the 
granules, x i ,000. 
Fig. 25. Transverse section of two sieve tubes with a lateral plate connecting them. Thick 
slime strings with median nodules and paired granules, x 420. 
Fig. 26. Transverse section, showing an inclined terminal wall crossing the lumen of the large 
sieve tube and dividing it into two separate elements. The granules are in various stages of sinking 
in and the slime strings are thick. Owing to the fact that the wall is inclined, many of the slime 
strings being cut obliquely are incomplete, and others have had their granules detached, x 600. 
Figs. 27 and 28. Transverse sections of a portion of a sieve tube abutting upon phloem paren- 
chyma cells. The pits each contain one, or more rarely two, protoplasmic threads. The median 
nodule is visible as a dark spot. The wall of the sieve tube is much thicker than that of the 
phloem parenchyma cell, so that the portion of the thread traversing the wall of the latter is very 
short and only just recognizable, x 600. 
PLATE LV. 
C — cortex ; E = endodermis ; P — pericycle ; PPh — protophloem ; Ph = phloem ; 
PPr = phloem parenchyma ; X = xylem. 
Fig. 29. Transverse section of young rhizome. The sieve tubes {Ph) are unthickened and 
the contents have fallen out. The protophloem elements are considerably thickened, and many of 
them still retain their contents, but no connecting threads are visible, x 470. 
Fig. 30. Transverse section of rhizome, old. A group of sieve tubes with lateral sieve plates 
connecting them. Traversing the sieve plates, the slime strings can be seen indistinctly. The 
refringent granules are visible as dark dots embedded in the walls in. connexion with each slime 
string, especially on the largest plate of the largest sieve tube A ; the pits connecting a sieve tube 
with a phloem parenchyma cell can be distinguished, x c. 500. 
Fig. 31. Transverse section of portion of mature rhizome. The distribution of the sieve tubes 
as a peripheral ring of elements, connected with one another by sieve plates on the radial walls, is 
shown. The position of the sieve plates is indicated, slightly diagrammatically, by the blue colour 
of callus. Protophloem is almost absent from this section, x 450. 
Fig. 32. Transverse section of portion of rhizome, old. The peripheral row of sieve tubes 
skirting the xylem is shown. The sieve plates on the radial walls are large, and in places the granules 
and slime strings can be seen, x c. 500. 
