Corky Excrescences on Stems of Zanthoxylum. 163 
given these a very careful examination. After describing their 
mode of origin, and attempting to determine the morphological 
value of the thorns, he states regarding the older stages: f These 
Cactus - spines quickly lignify ; they become fixed and prevented 
from injuring the tissues beneath by a resistent basal tissue. 
Thus, at the same time as lignification takes place, a cork- 
cambium-like tissue arises, which, in quick succession, pushes 
off layers of firmer substance, by which the spines are very 
firmly glued together V 
List of Plants whose Thorns have Basal Cork- 
Formation. 
In works on Descriptive Botany, all that is noticed on this 
head is whether the plant is thorny or not. And in the accom- 
panying illustrations no notice is taken of any peculiarities of 
bark in the older plant, the flower and young shoot alone being 
figured. A study of these works has been unproductive of 
results, with a few exceptions. 
In works devoted to the description of timbers and the bark 
of trees, it might be expected that the corky excrescences 
would be referred to ; and, in compiling the following list, a 
good many examples have been obtained from Gamble’s 
Manual of Indian Timbers. The majority of the cases have, 
however, been noted in looking over the specimens in Botanical 
Gardens and Museums, — in the latter case not always fully 
named. The list does not profess to be complete, but may 
serve as a basis for anyone interested in the subject, and will 
show sufficiently well the wide distribution of the phenomenon 
in question. My thanks are specially due to Mr. J. R. Jack- 
son, the Curator of the Kew Museums, for his assistance in 
allowing me free access to the specimens. 
Malvaceae. 
Eriodendron anfraduosum . Specimen in Kew Museum with spines 
half an inch long, over which the thin outer bark is continued. 
There is probably a corky contact base. 
1 Delbrouck, Die Pflanzenstacheln, Hanst. Bot. Abh. ii, p. 74, 1875. 
