56 Calvert and Boodle. — On Laticiferous Tissue 
to this part that the laticiferous tubes are confined. They 
usually occur in groups, each in the neighbourhood of a 
primary xylem-bundle (Figs, i and 3). 
Bounding each primary xylem-group internally a tissue 
is frequently found consisting of thin-walled cells, small in 
transverse section, but considerably elongated longitudinally ; 
these may be identical with the internal ‘cambiform’ cells 
described by Pax in several tribes of the Euphorbiaceae as 
representing rudimentary phloem 1 . They differ widely in 
shape from the thin-walled peripheral pith-cells described 
above, being longer and narrower, and rectangular in longi- 
tudinal section. The thin-walled pith forms an unbroken 
ring and lies inside these groups of cambiform cells. 
Longitudinal sections show that the laticiferous tubes in the 
pith have reticulate anastomoses similar to those described 
by Dr. Scott 2 in the cortex ; such a system could not arise 
from the branching of single cells. In the secondary phloem 
new laticiferous elements are continually being formed by the 
cambium, and in this region remains of the walls, separating 
the cells from which the laticiferous vessels are formed, were 
frequently found both by Dr. Scott and ourselves. In the 
case of the medullary tubes, stages in the absorption of the 
cell-walls could naturally only be observed near the apex of 
the stem, where the tissues have not yet passed into their 
permanent condition. Such stages were observed in parts 
of the stem about l\ millimeters in diameter at a distance 
of 15-20 mm. below the apex. Fig. 8 shows a tolerably 
simple case of cell-fusion, in which the remains of a partially 
absorbed wall are seen. 
Transverse sections through an internode show that the 
members of one group branch and anastomose freely among 
themselves, but do not anastomose with the members of 
other groups. The cortical tubes, on the contrary, form a 
continuous reticulate cylinder extending all round the stem 3 . 
1 Engler’s Bot. Jahrb. Bd. v. p. 401. 
2 Compare our Figs. 2 and 3 with Figs. 1 and 2 in Dr. Scott’s memoir. 
8 Quart. Journ. Microscop. Science, vol. xxiv. pp. 196-7. 
