248 Scoit and Sargant. — On the Pitchers of 
Laticiferous tubes, of the branched, inarticulated type 
usual in the Asclepiadeae, traverse both cortex and pith, and 
sometimes enter the phloem-strands. The pericycle is several 
layers of cells in thickness ; in its outer region there are 
numerous groups of sclerenchymatous fibres. The starch in 
the endodermal cells evidently serves to provide the material 
for the thickening of the cell-walls of the sclerenchyma ; it is 
very abundant before this process begins, and gradually 
diminishes as the thickening layers are deposited. 
That part of a lateral branch which bears the pitchers is 
considerably stouter than the stem generally. Where a 
pitcher is borne on one side of the branch, and an ordinary 
leaf on the other, the xylem is at least twice as thick on the 
side towards the pitcher, and on this side the amount of 
sclerenchyma is also enormously greater. 
The number of vascular bundles entering a rudimentary 
scale-leaf is usually four. The normal foliage-leaves and the 
pitchers receive about six or seven bundles each. The out- 
going bundles are accompanied by the internal groups of 
phloem corresponding to them, and are imbedded in con- 
junctive parenchyma continuous with that of the stem- 
cylinder ; the whole vascular system entering the petiole 
thus forms a meristele , in the sense of Van Tieghem 1 . 
Comparative Anatomy of the Foliage-leaf and the 
Pitcher. 
The orientation of the vascular bundles in pitcher and leaf 
completely confirms the morphological conclusions arrived at 
by Treub from his study of the development. 
The main bundles in both organs are bicollateral ; in the 
smaller bundles the internal or superior phloem becomes 
much reduced ; in the finest branches it disappears altogether. 
In the case of all except the finest bundles the orientation 
was therefore determined by the position of the protoxylem- 
elements. In the leaf these are of course always di ected 
1 Journal de Botanique, t. v. 1891, p. 284. 
