Cuscuta and its Host '. 663 
pith of Salvia} and such strands were quite common in C. rejlexa in the 
juicy pith of Begonia. 
The hyphae immediately surrounding the central core become applied 
to the xylem elements of the host; the strands of cells to which these 
hyphae give rise become organized as strands of reticulately pitted tracheides 
and are connected with the xylem of the main stem of the parasite. Con¬ 
cerning the details of the development of the xylem connexions I have 
little to say; Peirce has given some descriptions of the mature state in his 
paper, and my observations, as far as they go, do not differ from his to any 
important extent. The hyphae apply themselves firmly to the xylem 
elements of the host; and the thin walls at their tips, which are at first 
undifferentiated, later become lignified, thick and thin areas being developed 
which correspond to the thick and thin areas of the host wall. 
The peripheral hyphae of the haustorium (outer hairs of the brush) do 
not extend so far into the host plant, but many of them push their way 
straight through the older layers of the host phloem (Fig. 60, PI. L, is an 
example of a parasite hypha seen boring through a host sieve tube), and, 
making for the functional and developing sieve tubes from which the most 
nutriment can be obtained, become applied to their walls and form intimate 
connexions with them. It is generally found that in the phloem the 
haustorium expands considerably (especially in C. europaea on Vitis and 
C. sp. ? on Solidago). At the surface of the host the haustorium is circular 
in section; it becomes oval or lozenge shaped in the cortex of the host, the 
long axis of the oval being parallel to the length of the host stem. When 
it reaches the phloem it expands laterally and may again become roughly 
circular in section. Contact is thus made with a large number of sieve 
tubes outside the region originally pierced by the shaft of the haustorium. 
When a connexion has been made, the applied hypha becomes subdivided 
to form a strand of cells from which a string of short sieve tubes is 
developed ; these are connected by other short sieve tubes in the shaft of 
the haustorium with the phloem in the parasite stem (Figs. 62-4). It is 
the development of the phloem connexions and of the strings of sieve tubes 
with which I am mainly concerned. 
Some of the separate hyphae on the outer edge of the brush have 
got no further than the cortex, others have pierced a little deeper, but only 
as far as the old disused sieve tubes. It is not possible to determine how 
far these have still the power to work further into the functional phloem, 
but it seems most likely that at a certain stage their development stops, 
the total number of connexions being then adequate to the needs of the 
parasite. Occasionally a hypha after reaching the old phloem turns back, 
bending sharply on itself, and returns into the cortex. Such hyphae pre¬ 
sumably are unable to find food in the old phloem, and seek it in the 
1 Cf. also Peirce, 1893, p. 309, for development in an innutritions pith. 
