Cuscuta and its Host. 677 
normal mechanics of the sieve tubes of the host and ensures for the parasite 
a long-continued supply of nutriment. 
7. The facts accumulated afford evidence on three interesting theoreti¬ 
cal questions: — 
A. That the parasite takes so much trouble to make use of the host 
sieve fields as they are, and not to disturb the mechanics of the sieve tubes, 
is important testimony in favour of the functional efficiency of sieve 
tubes in general and sieve fields and sieve plates in particular. 
B. Various cases of hydrolysis of the cell-wall have been demon¬ 
strated ; not only are substances staining with callus stains formed in the 
ordinary way in the sieve tubes, but they occur in the fusing longitudinal 
walls of adjacent hyphae, in the dissolving walls at the tips of the hyphae, 
before junctions with the phloem are developed, and in the form of granules 
or masses of varying size in many of the cells of the old haustorium. 
Hydrolysis has not proceeded to the same extent in all these cases. In the 
first three places the hydrolysed substance is produced from already formed 
cell-wall; in the last place it is laid down directly by the protoplasm, and 
probably owes its origin to the superabundance of cellulose absorbed by the 
parasite. 
The haustorium of Cuscuta thus provides us with unmistakable cases 
of the formation of callus, both by direct deposition and by changes in 
already formed wall. 
C. Connecting threads are not found in the fusion walls between 
adjacent hyphae. Also the wall at the tip of a hypha is not burrowed 
through by connecting threads or slime strings when a junction with a sieve 
area is to be formed; but instead the whole area of the parasite wall 
abutting on the sieve fields is absorbed. These facts militate against 
Strasburger’s theory of the origin of connecting threads through boring out 
by the protoplasm, and may be regarded as indirect evidence in favour of 
Gardiner’s view that connecting threads only occur between genetically 
connected cells, their origin being associated with the processes of cell- 
division. 
Botany School, Cambridge, 
February, 1911. 
Bibliography. 
Benson, M. C.: Root-Parasitism in Exocarpus. Ann. of Bot., xxiv, 1910. 
Gardiner, W. : (a) The Histology of the Cell-wall, with special reference to the Mode of 
Connexion of Cells. Roy. Soc. Proc., lxii, 1898. ( b ) Methods for the Demonstration 
of ‘ Connecting Threads’ in the Cell-wall. Proc. Camb. Phil. Soc., ix, 1898. The Genesis 
and Development of the Wall and Connecting Threads in the Plant Cell. Roy. Soc. Proc., 
lxvi, 1900. The Mode of Formation of the Initial Cell-wall, &c. Proc. Camb. Phil. 
Soc., xiv, 1907. 
