66 Gregg. —Anomalous thickening in 
that the roots investigated retained their cortex, even in 
their oldest portions, only external periderm being formed 
(see De Bary, 1 . c. p. 613). The anomalous development 
consists essentially in the formation of additional cambial 
layers external to the normal one ; the process as observed 
appears under two modifications, one of which was only 
found in a single root, while the other occurred in all 
the remaining roots examined. The latter will be first 
described. In this case the abnormal development begins 
by the formation of cambial divisions in cells of the peri- 
cambium lying at a short distance from the ends of the 
normal cambial layer 1 . Other divisions soon begin both in 
the cells lying immediately outside the normal phloem, and 
in those immediately adjacent to the ends of the normal 
cambium; so that ultimately a complete cambial ring is 
formed, consisting on its inner side of the original normal 
cambium, and on its outer side of the more recently formed 
layer — it will of course be understood that as this process 
goes on on both sides of the root, two complete rings of 
cambium are formed. The anomalous portion of each of 
these rings produces numerous layers of xylem on its outer 
side and a considerable amount of phloem towards the interior. 
In this reversed orientation of the products of the first de- 
veloped anomalous cambium, lies the most characteristic 
peculiarity of the structures we are considering. As a result 
of this reversed orientation the tissue lying between the 
anomalous and the normal cambium becomes compressed 
(see Figures). 
At a somewhat later stage a second process of abnormal 
development begins ; this process, like the one last described, 
takes its rise from the pericambial tissue. In the cases where 
the very first origin of this was observed, the development 
began by divisions in the outermost layer of the pericambium 
lying immediately below the endodermis as shown in Fig. 2, 
and it is thus separated by numerous layers of cells from the 
1 See description of Figures. 
