560 
PROFESSOR H. MARSHALL WARD ON THE 
Explanation of Plates. 
PLATE 32. 
Fig. 1. Portion of Bean-root with, the tubercles or root-swellings of various ages, 
showing the different stages of development; a very young one is seen on 
the rootlet to the left above. (Natural size.) 
Fig. 2. One of the larger swellings cut in two. The buff-coloured portion is the part 
where the parasite is rampant: the paler portions towards the apex 
contain hyphae only. The narrow zone a at the apices of the lobes 
consists of meristematic cells scarcely affected as yet by the hyphrn. 
(Natural size.) 
Fig. 3. Half-diagrammatic section of a root, with tubercle and normal lateral rootlet. 
The latter arises opposite a xylem strand. The tubercle originates in the 
cortex, and also (in this case, but not always) opposite a xylem strand. 
The various tissues of the tubercle are indicated. The apical meristern 
contains very few hyphse : numerous branched liyplue are found in the 
cells lower down; the dark-shaded cells in the lowest central parts are 
hypertrophied and tilled with the bacterium-like corpuscles—genunules 
or yeast-cells. 
Fig. 4. Three cells of the dark inner portion of the tubercle (fig. 3). The corpuscles 
(gemmules) have multiplied to an enormous extent, causing the protoplasm 
to become vacuolated and plasmodium-like, and the cells to enlarge : the 
dark body embedded in the mass of yeast-cells and protoplasm is the 
nucleus. E/4. 
Fig. 5. Similar cells after the macerated tubercle has rotted : the cells are separating, 
and appear full of bright (dark) granules in a matrix. The granules are 
the now dormant yeast-corpuscles (gemmules); the dark body is the 
nucleus of the cell. E/4. 
Fig. 6. The gemmules—granular bodies in tigs. 4 and 5—more highly magnified. 
a and b are from still active tubercles, and are more highly magnified 
than c, which is from an old tubercle of the preceding year, a and b = L/4 ; 
c = J/4. 
Fig. 7. Transverse section across a rootlet, and tubercle about the size of the smallest 
one in fig. 1. The tissues of the tubercle are seen to have hyphm in 
them ; these hyphse are branches from the thicker hypha which passes 
down the root-hair a (to the left of the figure) and across the cortex of 
the rootlet. (B/3.) 
Fig. 8. Portion of fig. 7 more highly magnified, and showing how the hypha from the 
root-hair commences to break up into branches as it passes into the young 
tubercle. (B/4.) 
