98 
Peirce . — A Contribution to the 
base is of course the inner one and is more or less closely 
applied to the stem, consists of rather small thin-walled 
epidermal cells whose continuity is rarely broken by stomata. 
Immediately underlying this layer are the usual spongy 
parenchyma-cells which make up the larger part of the 
thickness of the leaf. At fairly regular intervals groups of 
these cells, about ten in each group, immediately underlying 
the epidermis, become more thick-walled and elongated, 
forming slender strands running lengthwise in the leaf, and 
thus adding something to its strength. The parenchyma-cells 
in the centre are large, thin-walled, spheroidal, and are 
adjoined by parenchyma-cells of similar character except that 
they are smaller in proportion as they are nearer the surfaces 
of the leaf. The under part of the leaf, the outer owing to 
its vertical position in embracing the stem, contains the large 
vascular bundles, whose course is longitudinal. These bundles 
project into the mesophyll, are separated from one another 
by considerable masses of parenchyma, and are surrounded 
individually by strongly lignified sheaths. The endodermis 
of each bundle is continuous with a plano-convex mass of 
sclerenchyma- cells which abuts by its plane side upon the 
epidermis. The epidermis of the lower side of the leaf con- 
sists of smaller cells with thicker walls, and is more frequently 
broken by stomata, than the epidermis of the other side. 
Except directly opposite the vascular bundles, where it 
adjoins the masses of sclerenchyma-cells, this lower epider- 
mis, like the other, is in contact with the mesophyll- 
parenchyma. 
Turning now to the parasite, we notice that the papillate 
cells of the epidermal cushion, which overlies the developing 
haustorium, have become so firmly applied to the epidermis 
of the leaf that their tips are flattened. The diameter of the 
whole cushion is about twice as long as the distance between 
two vascular bundles in the leaf. The young haustorium, 
developing in the cortical matrix of its parent, will be 
variously influenced by the resistance offered to the pressure 
which by its growth it exerts, and it will naturally, other 
