682 Tho day.—Histological Relations between Cuscuta and its Host. 
arrows pointing to P and H indicate the direction of the ends of the haustorium which belong 
respectively to parasite and host; the element cut in transverse section belongs to the phloem of the 
main parasite stem. Callus changes have taken place to an unusually large extent in the longitudinal 
walls, x 600. 
Fig. 64. Strand of sieve tubes from the haustorium of C. europaea on Vitis (preserved in 
October). Accumulation of callus had taken place over the. sieve areas on the subdivision walls, 
but none was found on the original walls of the hypha. W — wall of the original hyphal element 
which has now become subdivided. C = crushed cells on the periphery of the invading strand. It 
was not found possible to make out the exact relations of parasite and host, x — a thin ridge or 
broken wall. (Cf. Figs. 68, 76, &c.) x 500. 
Fig. 65. Ends of three invading hyphae, closely appressed to one another ; the left-hand element 
resembles Figs. 58, 59, &c. ; the right-hand one is applied to a lateral sieve field of the host, x is 
probably the partially dissolved remains of the parasite wall, x 600. 
Fig. 66. An invading hypha in contact with a host sieve tube, of which a lateral sieve field 
is seen in surface view, x 600. 
Fig. 67. Compare Fig. 62. The end wall of the parasite cell beyond x has probably been 
dissolved, and the blue mass may represent part of its degenerating remains. The naked protoplasm 
of the parasite is seen extending beyond the blue mass, and would appear to have applied itself 
closely to the host sieve area, x 600. 
Fig. 68. Two invading elements which have turned more or less at right angles to their original 
course and are now running in almost the same direction as the host sieve tubes. The lower one is 
as yet unattached; two small blue-staining granules are seen embedded in its protoplasm. (Cf. 
Figs. 73-5.) The upper element has applied itself to a lateral sieve plate. No cell-wall could be 
distinguished between the sieve plate and the parasite protoplasm at X. (The preparation was 
stained first with safranin and London blue; afterwards light green and Delafield’s haematoxylin 
were used successively as wall stains.) x 500. 
Fig. 69. From a transverse section of C. sp. ? on Solidago sp. ? The tip of an invading parasite 
hypha is applied to a lateral sieve plate, and no cell-wall appears to be present between the sieve 
plate and the parasite protoplasm, x 600. 
Fig. 70. An empty parasite element whose wall appears to terminate in a ridge at X. J = the 
host sieve field to which the protoplasm of the parasite element was probably applied, x 500. 
Fig. 71. An empty parasite element applied to a sieve field, j. The remains of the wall (stained 
blue) at the tip X are apparently dissolving. x 600. 
Fig 72. From a paraffin preparation stained only with Delafield haematoxylin. The invading 
element with its enormous nucleus is applied to the sieve field j. In this case it was fairly clear that 
the parasite wall terminated on either side of the sieve plate at x x 750. 
Figs. 73, 74, 75. Haustorial cells showing blue-staining masses in various stages of development 
embedded in the protoplasm. All from old haustoria. x 750. 
PLATE LI. 
Figs. 76, 77, 78. 1 The ends of three invading hyphae which have formed connexions with sieve 
areas in the host phloem. Figs. 76 and 77 were obtained from a preparation stained with safranin, 
aniline blue, and London blue. The preparation was afterwards stained in Delafield’s haematoxylin, 
and Fig. 78 was drawn from the same three elements. The difference in proportion between the 
same element stained in the two ways is partly due to different foci, and the difference in thickness 
of the walls to the difficulty in focusing sharply walls which are unstained. 
The protoplasm of the parasite cells is only shrunk very slightly from the sieve plate, and it is 
fairly clear even from Figs. 76 and 77 that no wall intervenes between it and the sieve plate. This 
is made unquestionable by Fig. 78, the small space remaining quite unstained. In Figs. 76 and 77, 
x represents what was regarded as being probably the termination of the parasite wall. In Fig. 78 
these points are more sharply identified. H = host sieve tube, p = parasite element. J = sieve 
field of host. W = wall seen obliquely. F = line of fusion between walls of adjoining parasite 
elements. R = remains of almost dissolved parasite wall. In Fig. 78 the host walls are shaded, 
the parasite walls left unshaded. Fig. 78 magnified 1,000, Figs. 76 and 77 slightly less. 
1 Fig. 78 ; D. Thoday del. 
