Hill . — The Histology of the Sieve-Tubes of Angiosperms . 263 
sieve-tubes of the protophloem of Vitis . In the secondary phloem of Vitis 
and many other plants the end-walls are inclined and bear several sieve- 
plates, 1 so that in a transverse section the sieve-plates appear to be borne 
on the radial walls of the tubes. 
Phloem : General Anatomy. 
The general anatomy of the phloem varies considerably in different 
plants. In Vitis f which has been so carefully studied by Wilhelm, and also 
in T ilia (cf. Perrot, pp. 127, 128), the phloem is composed of alternating 
bands of sieve-tubes, together with their companion cells and parenchyma, 
and of bast fibres. 2 In Wistaria the alternation of fibres amongst the 
Fig. 4. Vitis. Phloem in transverse section, showing the alternating bands ( s .) of the sieve- 
tubes ( s . t.) and cotapanion cells (c. c .), and the bast fibres (/.) ; the edge of a medullary ray is seen 
on the right. (Copied from Wilhelm, PI. I, Fig. i.) 
sieve-tubes is less regular, but the latter show an interesting feature in 
always having their sieve-plates at about the same horizontal levels. This 
characteristic makes Wistaria a useful plant for research, since a single 
favourable transverse section will show sieve-plates in every stage of 
development. Viscum is peculiar in that its sieve-tubes and companion 
cells are grouped in lenticular areas, as seen in a transverse section, which 
1 Wilhelm, 1. c., PL II, Fig. 16, &c. ; Perrot, 1. c., Fig. 39. 
2 Ibid., PI. I, Fig. 1. 
