Cuscuta and its Host. 679 
Fig. 3. Terminal sieve plate at about the same stage, but more deeply pitted, and with slime 
strings more bored out. x i ,000. 
Fig. 4. A lateral plate, similar to the terminal plate in character, x 500. 
Fig. 5. A terminal plate in which the formation of callus has extended over the part of the wall 
in between the pits, x 500. 
Fig. 6. An old terminal sieve plate, with a large deposit of callus on either side. The majority 
of the sieve tubes in the material were at this stage, x 500. 
Fig. 7. Lateral sieve plate in surface view, x 1,000. 
Fig. 8. Lateral sieve plate in section ; in each pit is a single slime string surrounded by a callus 
rod, which is interrupted at the middle lamella by a median node, x 1,000. 
Fig. 9. Sieve field in section. The wall is profusely pitted ; each slime string has its own callus 
rod ; the median nodes are clearly shown, x 1,500. 
Fig. 10. Ditto. Shows more uniform pitting; each pit is occupied by a group of callus rods. 
Most of the plates to which the haustorial cells apply themselves resemble this figure. (London 
blue only.) x 750. 
Fig. 11. Surface view of sieve fields. The small figure shows a few of the slime strings, each 
traversing a hole in the wall, and surrounded by a tube of callus, x 800 and 1,500. 
Fig. 12. Sieve field; in which the formation of callus has extended over the areas of wall 
between the threads, x 800. 
Fig. 13. Sieve field over which large masses of callus have been deposited, x 800. 
P'ig. 14. Longitudinal section of wall of developing xylem element, showing the pit-closing 
membrane in section, traversed by a group of threads, x 1,500. 
Fig. 15. Wall of the same. M = pit-closing membrane with ends of threads in surface view; 
P = pit in section showing pit filling, x 1,000. 
II. Cuscuta. 
(Preserved June or July unless otherwise mentioned). 
Fig. 16. Radial wall of cortical cell of C. rejlexa , showing the connecting threads traversing 
the pit-closing membranes, x 1,500. 
P'ig. 17. Longitudinal wall of cortical cell of C. europaea. x 1,000. 
Fig. 18. Cortical cell of C. rejlexa in section, showing the groups of threads traversing the pits 
in the longitudinal walls seen both in surface view and in section, and also the much smaller groups 
in the transverse walls, x 1,000. 
Fig. 19. Longitudinal section of sieve tube and companion cell from the main stem of C. rejlexa. 
The threads in the transverse wall are arranged in groups and are still unaltered. In the right-hand 
longitudinal wall (between two sieve tubes) the wall surrounding them has become changed into 
callus, in the left-hand one (between sieve tube and companion cell) the change has only occurred in 
the sieve-tube side of the wall. cc.= companion cell, x 1,000. 
Fig. 20. Terminal sieve plate of sieve tube of main stem of C. rejlexa ; each thread has given 
rise to a slime string enclosed in a callus rod. Fig. 20 A illustrates the stages in the development of 
the slime strings as seen in longitudinal section, x 1,000. Fig. 20 B is part of an old transverse 
plate in longitudinal section, showing the fully developed callus rods interrupted at the middle 
lamella by a well-marked median node. X 1,500. 
Fig. 21. A sieve tube from the main stem of C. europaea, showing a case in which the strings are 
arranged in groups and not distributed uniformly, x 600. 
Fig. 22. Sieve tube and companion cell from main stem of C. rejlexa. The surface of the wall 
in between the individual callus rods is now coated with a thin layer of callus. In the wall between 
sieve tube and companion cell the callus change appears only to occur in the sieve-tube side of the 
wall, cc.— companion wall, x 1,000. 
Fig. 23. Fully developed sieve plate as Fig. 22; slime strings more bored out. x 1,000. 
Fig. 24. Old sieve tube from C. europaea (preserved in October), showing accumulation of 
callus on one side of sieve plate and over the sieve-tube end of the groups of strings in the longitudinal 
wall between sieve tube and companion cell, cc. — companion cell, x 600. 
Fig. 25. Surface view of a transverse sieve-plate from the haustorium o VC. rejlexa ; the callus 
rods are evenly distributed and each contains a single slime string, x 1,500. 
