of some Phanerogamic Parasites . 303 
removed from the surface of the stem of the host, only a 
small amount of food is taken from it and the conducting 
tissues are weak. The xylem, already bifurcated in order to 
unite with the two larger outer bundles, sends a feeble strand 
of tracheids from each of the adjacent sides of the branches. 
Probably also two feeble strands of sieve-tubes and companion- 
cells are sent out from the two phloems, but no callus-plates 
are shown by the aniline-blue test. In such cases the 
haustorium consists near its tip of two quite separate collateral 
bundles ; a little further back of four such bundles ; still 
further back of only two ; and throughout the most of the 
shaft of only one bi-collateral large bundle. Where the 
haustorium impinges upon the ring of confluent fibro-vascular 
bundles in the other species of Mimoseae and in Thevetia 
7ieriifolia both phloems are of course active and the xylem 
does not need to divide. 
Having studied the origin, development, and structure of 
the haustorium we are ready to answer the question of its 
morphology. De Bary says 1 : ‘ Roots are found as lateral 
branches on members of their own kind, as well as on stems, 
rarely on leaves ; some appear in definite morphological 
positions.’ ‘ The invariably endogenous formation of lateral 
roots takes place in or close to vascular bundles or masses of 
wood or bast. Their vascular bundle is inserted directly and 
without branching on the nearest one of the main axis, or it 
divides into branches, which connect themselves with several 
bundles of the axis.’ The typical primary bundles of roots, 
as is well known, are of the radial type, secondary changes 
causing the thickening roots to assume the structure of 
ordinary stems wi£h collateral bundles. We have seen that 
the central cylinder of the haustorium consists at first of 
procambium surrounded by unmerismatic parenchyma ; that 
this procambium changes in the centre into a xylem, and 
on either side of this into a phloem ; that parts of the 
procambium persist for a time as cambiums between the 
A. De Bary, Comp. Anat. of Phanerogams &c., p. 315. Clarendon Press, 1884. 
