304 Peirce. — On the Structure of the Haustoria 
xylem and the two phloems ; that there is never at any time 
a radial structure ; and that its bi-collateral bundle is con- 
nected with two axial bundles of the mother stem. The 
haustorium, originating in the cortex near the pericycle from 
a definitely marked mass of cells, is formed from them by 
successive division. No other cells from the cortical paren- 
chyma or the epidermis add themselves to it. This is clearly 
proved by the figures already described. The haustorium of 
C. americana differs decidedly, therefore, from the haustoria 
of C. epilinum and C. epithymum as described by L. Koch l . 
(I shall have occasion to refer later to the origin and structure 
of the haustorium of these two species.) We see then that 
the haustorium of C. americana is, so far as its origin .shows, 
a lateral root ; so far as the bi-collateral structure of its 
bundles is concerned it does not conform to the typical 
structure of a root. We must consider it to be morpho- 
logically a root, but that it has become modified in structure 
to do its work the better. 
We come now to the morphology of the parts of the 
haustorium. The layer of cells forming the surface of the 
haustorium, though not differing greatly from those immedi- 
ately underlying it, is sufficiently different, especially near the 
tip, to justify the name of epidermis being applied to it. In 
the young haustorium (see Fig. 5, PI. XIII) it should receive 
the name of dermatogen. The cortex, consisting of several 
layers of cells at the base, is reduced to a single layer at the 
apex of the haustorium. It evidently originates from a 
periblem. What I have so far called the central cylinder 
plainly corresponds to the plerom. At the tip of the young 
haustorium these three layers can no more and no less be 
distinguished from one another than at the tips of most young 
roots. The growing-point of the haustorium corresponds in 
position (see Fig. 5, g, PI. XIII) and in character with the 
growing-point of typical roots. It is covered by a single 
layer of cells which, in all but the youngest stages, I have 
called collectively the Sticker . But the sucker is merely 
1 L. Koch, Die Klee- und Flachs-seide. Heidelberg, 1880. 
