TUBERCULAR SWELLINGS ON THE ROOTS OF VICIA FABA. 
545 
slowly becomes very hard and wrinkled, turning dark-brown or almost black in the 
process; it is not easy to cut such tubercles. Their consistency is that of stiff horn, 
and the razor “drags” unpleasantly in the section. Thin sections placed in water 
swell for several days, and the contents of the cells are, as before, densely crowded 
brilliant corpuscles in a matrix, which is bright yellow in chlor-zinc iodine. These 
corpuscles are particularly minute, and like mere points in the section. 
In the cells containing these corpuscles the presence of hyphge is to be observed 
(figs. 12 and 15-18); even in the cells of tubercles which have been dried for a year, 
and are hard as horn, a few minutes’ maceration in very dilute ammonia enables one to 
detect these hyphge (fig. 18), which are obviously those described by Frank. These 
hyphge are very curious. In the cells filled with corpuscles they are short, often much 
branched, extremely delicate, and apparently springing from the cell-walls, though 
really coming from hyphge running in and through the substance of the cell-walls 
(figs. 12, 17). 
Sections through young and actively growing tubercles show that the hyphge branch 
and pass from cell to cell throughout the meristem of the interior (figs. 7-18). In 
very young tubercles the cells contain only these hyphge ; subsequently, when the 
tubercle reaches the dimensions of a mustard-seed, the tiny bacterium-like bodies begin 
to accumulate. 
In sections through very young tubercles, made transversely to the long axis of the 
root, and passing axially through the tubercle, I have observed the following facts. 
A fairly strong hypha, several times thicker than the cell-walls in many cases, can be 
traced through from the epidermis to the origin of the young tubercle (figs. 7, 8, 9); 
the tip of the tubercle is always directed so as to meet this hypha. 
I had frequently satisfied myself of this fact, before more fortunate preparations 
showed the facts explained by figs. 9 and 13. Here, as is seen, the hypha referred 
to passes down the cavity of a root-hair, and thence traverses the cortex of the root, 
cell by cell, beginning to branch when it enters the mass of tissue which constitutes 
the young tubercle. It is more difficult to see the branches in the meristem of the 
tubercle, for two chief reasons : the cells are smaller and more numerous, and their walls 
are very thin. Moreover, their protoplasm and nuclei are very bright. Nevertheless 
the difficulty is only relative, and, as already stated, Frank had already seen the 
hyphse passing from cell to cell inside the tubercle, though he did not trace them far. 
The isolated thicker hypha in the epidermis and cortex (figs. 8, 9) offers more 
distinct characters than the finer ramifications which it makes further inwards. The 
hypha is without septa, so far as can be made out by reagents of all kinds. It has a 
very delicate membrane, which is quite distinct in specimens treated with osmic acid 
or with chloral hydrate, or hardened in alcohol, &c. It passes straight across the 
lumina of the cells, through wall after wall, on its way towards the centre of the 
root; but a curious and very characteristic feature is the trumpet-like enlargement 
of the hyphge at the spots where they pierce the walls (figs. 9-14). This has been 
MDCCCLXXXVII.—B. 4 A 
