256 
On Dodder. 
cranberry, heather, centaury, scabious, grass, and even on the 
brake. It is also found living on plants that are themselves 
partial parasites, like eye-bright, yellow-rattle, and bastard toad- 
flax. 
Figs. 2-4 show the anatomical relation of Cuscuta epithymum 
to the supporting plant. Fig. 2 represents the Cuscuta twining 
round the stem of Centaurea scabiosa, Linn. — the Great Knap- 
weed. At F the stem of the knapweed and the dodder is cut 
through, and this section is magnified ten times in the diagram. 
Fig. 3. The oblong portion indicated by the letters A B C D 
is still further magnified in Fig. 4, so as to show all the details 
of the structure. In the centre, the stem of the knapweed is shown 
cut across, exhibiting the cells of the pith, surrounded by the 
vascular and wood bundles, and these again enclosed by the bark. 
Three cones from the coil of the dodder penetrate the knapweed, 
peaching to the pith. These cones consist of the outer cellular 
covering of the stem, with a prolongation of the wood structure 
passing down their centre. Two suckers are shown pushing 
themselves out from the free portion of the stem of the dodder. 
The principal figure is from Chatiris's ' Plantes Parasites.' 
The structure of the dodders, and the nature of the relation 
between them and the plants on which they are parasitic, have 
been investigated by Mirbel, Unger, and especially by Chatin. 
Being complete parasites they are without the food-producing 
or food-procuring parts of ordinary plants, viz., roots and leaves. 
Nor have they any of the green colouring matter (chlorophyl) 
which plays an important part in elaborating the food of vege- 
tables, yet not an essential part, as is shown by the experiments 
of Saussure and De Candolle on Atriplex hortensis rubra, and 
Ulva purpurea. The minute scales and flower bracts, which are 
the only representatives of the leaves, are, as well as the stem, 
completely destitute of stomates. 
The stem consists of a cellular pith surrounded by a wood 
structure, which differs, however, from the wood bundles of 
other dicotyledonous plants in being destitute of ducts, of medul- 
lary rays, and of liber. There is, consequently, no true bark ; 
its place is occupied by a cellular layer surrounding the wood 
cylinder, the cells of which contain a red liquid, and are more 
or less charged with starch granules. 
The suckers are developed from the stem. The flattened 
portion is derived from the external layer of cells. Through 
this is pushed a cone composed of the cellular pith and wood 
structures of the axis. These penetrate the stem of the sup- 
porting plant. It is not easy to understand how these delicate 
cell structures penetrate the firm fibro-vascular tissues while 
they are in active life. The same problem presents itself in 
