GO 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
(3) Structure of Tissues. 
Thickening of the Wall of Cambium-cells.* — Herr F. Kruger has 
made a series of observations on this subject, chiefly on Sambucus nigra , 
though the results were essentially the same in all cases, whether with 
Dicotyledons, Monocotyledons, or Gymnosperms, woody, herbaceous, 
succulent, or annual plants, aerial organs or roots. 
The thickenings, which appear lens-shaped in tangential sections, 
are bands on the radial walls ; they are separated from one another by 
roundish pits which do not include the whole breadth of the wall, and 
correspond to the thin spots on the tangential section. Though less con- 
spicuous than in the winter, they are present also in the summer. These 
thickenings occur not only in the closed cambium-layer, but also in the 
cambium-plate of the still isolated bundles, and can be followed back into 
the procambial bundles. They are to be met with also in the whole of the 
young growth, and in the bast-parenchyme. In the cells of this tissue 
there is a differentiation between the outer and inner portion of the 
thickenings, due to the formation of mucilage, and intercellular spaces 
may arise. 
The sieve-plates and the sieve-plate system of the longitudinal walls 
are derived directly from the thin spots of the cambium. Both simple 
and bordered pits appear on the radial walls of the vessels, tracheids, 
and prosenchymatous xylem-cells, as also directly from the thin spots of 
the cambium. On the other hand the sieve-plate system of the tangen- 
tial walls of the sieve-tubes, and the simple and bordered pits on the 
tangential walls of the prosenchymatous xylem-cells, tracheids, and 
vessels, are secondary phenomena, and have no direct connection with 
the thickenings of the cambium. 
Resin-canals of the Leaves of Abies pectinata.f — According to 
M. J. Godfrin there are always, in the branches of Abies pectinata , eight 
longitudinal secreting canals situated in the cortex, and belonging to the 
stem ; these he calls the cauline canals. In their lower part these canals 
branch abundantly. In the very young spring-branches, or at the 
summit of those which are of a greater age, the canal-system of the leaf 
is separated from that of the stem ; but later, without its being possible 
to indicate any exact time, the foliar canals unite with those of the stem 
by means of ramifications proceeding from the latter. The author 
regards the foliar canals of Abies pectinata as homologues of the resinous 
glands of the Cupressineae. 
Root-system of Mikania scandens4 — Mr. W. W. Rowlee describes 
a peculiar structure in the root of this plant. In sections are seen four 
modified cells, two of which belong to the endoderm, and two to the row 
of cells just outside. These cells always lie in contact with the phloem- 
cells, and are so arranged as to enclose a rectangular intercellular space 
of considerable size and definite shape. They have large nuclei, which 
are always on the side of the cell next to the intercellular space ; and 
these spaces extend to very near the growing-point of the root, thus 
♦ Bot. Ztg., 1. 0892) pp. 633-40, 649-57, 665-73, 681-8, 702-8 (1 fig.). 
t Bull. Soc. Bot, France, xxxix. (1892) pp. 196-9. 
\ Bot. Gazette, xvii. (1892) pp. 276-7. 
