Cuscuta and its Host. 
6 73 
Again, there is the blue-staining mucilaginous substance which helps 
to fuse together the lateral walls of the separate invading hyphae during 
the process of the formation of a compact tissue. 1 This only stains with 
London blue, and does not show in preparations in which water blue 
only has been used. It is probably less hydrated than the sieve-tube 
callus. 
Still more important is the substance formed from the tips of the 
walls of the invading hyphae, on their way to apply themselves to the 
host sieve areas. It is this blue-staining substance in the tips which 
dissolves at the junction sieve plate by a process which is perhaps best 
described as mucilaginous degeneration of a limited area of the cell-wall. 
Sometimes this substance stains with water blue, more often with London 
blue only, but it has none of the bright, refractive appearance of ordinary 
callus. Both here and in the lateral walls the mucilage is clearly de¬ 
rived from the already formed cell-wall, probably by the hydrolytic action 
of a ferment in the hyphae. 
A substance staining with callus stains is found in still another form 
as granules, which often accumulate to form large blue-staining masses, 
very conspicuous, especially in the old haustoria. These granules are 
bright and refractive, staining both with water blue and London blue. 
Very few, if any, were found in the haustoria of C. reflexa or Begonia , 
but they were common in C. europaea on Vitis, and still more numerous in 
C. reflexa on Salvia. They never occurred in the main stem, but were 
found both in the sieve elements and in the parenchymatous cells of the 
haustorium, chiefly where it abutted on the pericycle and phloem of the 
host. They did not appear in the early stages of the growth of the haus¬ 
torium, but increased in number later. In C. reflexa on Salvia they were 
particularly numerous in the part of the haustorium near the pericycle of 
the host and were found also in the haustorial cells which had invaded the 
cortex and pith. They even occur, though then generally small in size, in 
the tips of the invading hyphae (Figs. 68, 73, PL L). In the old decayed 
haustorium they were very numerous, often swelling during the processes of 
staining, &c., and making the preparation obscure. Occurring in the midst 
of the protoplasm without relation to the cell wall, they must be formed by 
direct deposition from the protoplasm itself 2 (Figs. 73, 74, 75). 
They are probably of the same nature as the granules recently 
described by Dr. Benson in the 4 phleotracheides ’ of Exocarpus and 
Thesiump which also stain with water (aniline) blue. In these plants the 
granules apparently never attain the great size of those in Cuscuta. It has 
already been suggested that they are due to the deposition of the hydro- 
1 Ante , pp. 664, 665. Cf. the ‘ callus ’ which unites the separate members of a tetrad of pollen 
grains, by the solution of which the four grains are set free. Mangin, 1892. 
2 Cf. Hill, 1901 b, p. 599, and Fig. 26, PI. XXXIII. 3 Benson, 1910, pp. 673 ff. 
