in the Root mid Stem of Dicotyledons . 289 
occurrence of concentric belts of parenchyma in the wood, 
Kruger 1 confirmed Prof. Oliver’s results as to the medullary 
rays and was the first to discover concentric bands of typical 
phloem in the wood. This remarkable anomaly he was 
inclined to refer to the action of successively renewed cambial 
layers. Lastly, Solereder 2 confirmed Kriiger’s discovery, and 
found, in the occurrence of tangential divisions between the 
xylem and interxylary phloem-zones, a clear proof that the 
wood as a whole (Holzkorper) owes its origin to the appear- 
ance of successive cambial layers. Both he and Kruger, how- 
ever, recognise the possibility that the interxylary phloem 
might arise as in Strycknos, i. e. as De Bary erroneously sup- 
posed to be the case in Strycknos. On this view the inter- 
xylary phloem would be formed centrifugally on the inner side 
of the cambium. We proved in our former paper 3 that the 
phloem in the wood of Strycknos is developed centripetally, and 
it was the apparent analogy of structure between that genus 
and Acantholimon , which led us to examine the latter. Some 
divergences in detail, between our observations and those of 
previous writers, may well be due to specific differences. 
Acantholimon glumaceum is well known in gardens as a 
rock-plant. Its habit is not unlike that of its British relation, 
Armenia vulgaris . The latter, however, does not share its 
anomalies of structure. 
The diagrammatic transverse section (Fig. 16) will give a 
sufficient idea of the extraordinary structure of a thick stem. 
In order to understand the complicated conditions at maturity, 
it will be necessary to trace the development. 
The young stem has a perfectly normal structure. The 
bundle-ring is interrupted by several (usually 3-5) broad radial 
strands of parenchyma. The tangential section shows that each 
of these rays occurs immediately above the exit of a leaf-trace 
bundle. We do not see that they differ essentially from the 
primary medullary rays of other stems, which in all cases are 
1 Otto Kruger, Beitrag zur Kenntniss der sogenannten anomalen Holzbildungen. 
Dissertation. Leipzig, 1884. 
2 Loc. cit., Iiolzstructur, p. 164. 3 Annals of Botany, vol. III. 
