580 TKANSACTIONS AND TROCEEDINGS OF THE [Sess. lvii. 



of which they are branches, bear, in the season following 

 that in which they appear, accessoiy branches arising 

 immediately below them, and similar in character to the 

 indefinite branches above described as terminating: in a 

 spine. 



According to Delbrouck (ii.), the spine-branches of 

 TJlex persist in the cultivated state of the plant, while 

 those of Pruiivs, etc., disappear ; and he draws the 

 conclusion that the spines of TJkx are specially evolved 

 organs of the plant, while those of Pnvnus are due to 

 degeneration of branches which, under more favourable 

 nutritive conditions, continue to grov/ in length. 



As long as either the main stem or its branches remain 

 green and bear leaves the surface is marked by eiglit 

 longitudinal grooves, which run alternately with eight 

 ridges along the stem, the latter terminating one at the 

 base of each leaf, while a new ridge commences above the 

 median plane of the same leaf and runs up the stem 

 through eight inter nodes, the spiral being a y one, till it 

 reaches the under side of the base of the ninth leaf. All 

 these ridges are covered with long soft hairs, both on their 

 backs and along, at least, the upper part of their sloping 

 sides. 



In the autumn following that of the season in which 

 any given branch is produced, the ridges, along with all 

 the chlorophyll-containing tissue, are cut off' by means of 

 a phellogen formation, which takes place in the deeper 

 layers of the branch. The outer parts, though dead, still 

 adhere to the stem for some considerable time, but 

 ultimately fall away, leaving it brown and covered with 

 loose, thin scales of cork. 



The spines borne on the apices of spine-branches or at 

 the extremities of accessory branches are generally roughly 

 triangular in section, and are always green ; but no 

 phellogen formation takes place here, and the whole spine 

 ultimately dies, but in most cases adheres to the stem in 

 a dry state for a considerable period after all trace of life 

 has disappeared. 



The flowers are borne at the extremities of short 

 peduncles, each of which is provided with a pair of very 

 small lateral pro[)hylls, and arises in the axil of a spine- 



