6io 
Hill . — The Histology of the 
( b ) and ( b ') ferment action is taking place by means of a ferment which has 
originated in the tube ( B ). The presence of the ferment is indicated by the darker 
staining of the half-threads. The sieve-plates show secondary pits, and in the 
older membranes (c) slime-strings and callus-rods have been formed (stained with 
safranin). (x 750.) 
Fig. 10. Tangential section of a young sieve-tube before the appearance of the 
callus, fine protoplasmic threads cross the sieve-plates, (x 750.) 
Fig. 11. A mature sieve-plate in transverse section, the crenulated pit-closing 
membrane with slime-strings is clearly seen, also the median nodules. The callus- 
rods are not indicated (stained with safranin). ( x 750.) 
Fig. 12. Transverse section of the phloem in the region of the boundary cells, 
showing young albuminous cells of the medullary ray with pits between them and 
sieve-tubes. 
The pit-closing membrane ( a ) is thin with fine protoplasmic threads, whilst 
in the next cell secondary changes have occurred ; and the threads on the albuminous 
cell-side of the middle lamella are protoplasmic, whilst on the sieve-tube side they 
are slime-strings (stained with safranin). ( X 1000.) (Cf. Fig. 12, PL XXXI.) 
Fig. 13. Tanius communis , endosperm. A section of the cells of the endosperm 
bordering on the developing embryo ; ferment action is seen to be taking place 
and various stages are figured ; in some places the ferment is just entering the wall, 
in others a good deal of disorganization at the lamella has occurred. The entry 
of the ferment from one side is well seen. (From a section prepared by W. Gardiner 
and stained with safranin in 1896.) ( x 750.) 
Fig. 14. An old callus-cushion in transverse section, showing numerous threads 
which have become broken up into granules, (x 750.) 
Fig. 15. A. A young sieve-plate in surface- view, showing the ends of the slime- 
strings as fine dots in a few rather large sieve- fields. 
A'. The same plate in optical section, showing smaller and more 
numerous fields with dark dots which are the median nodes of the slime-strings. 
(x 75°0 
Fig. 16. A common appearance of mature sieve-plates as seen in optical section. 
The appearance of sieve-fields is given by the darkly stained, irregular, median 
granules, and the nodes of the slime-strings are visible as dark dots ; cf. with Fig. 1 1. 
PLATE XXXIII. 
In all the figures of this plate the callus is indicated by a blue tint to represent 
the colour obtained after staining with water-blue. 
Fig. 17. The callus is seen arising on one side of the membrane, and the 
accompanying alteration in the character of the threads is also indicated. 
( x 750.) 
Fig. 18. A further stage in the process, for here the callus-rods have reached 
the middle lamella, and the median nodules have been formed. Cf. PI. XXXI, 
Fig. 9. 
Fig. 19. The callus arising on each side of the membrane. 
Fig. 20. A mature sieve-plate, showing callus-rods, slime-strings, and median 
nodules. (Stain, safranin and water-blue.) ( x 75 °*) 
Fig. 21. A mature sieve-plate, showing the callus- rods stained with water-blue 
alone, (x 1000.) 
