The Anatomy of Rhododendron ponticum, L., and of 
Ilex Aquifolium, L., in Reference to Specific 
Conductivity. 
BY 
MAUD F. RIVETT, B.Sc. 
With seventeen Diagrams in the Text. 
HIS paper is the result of an investigation into the anatomical 
A characters of Rhododendron ponticum and Ilex Aquifolium with the 
object of ascertaining the anatomical basis for variations in the water-con- 
ductivity of the wood. 
In experimenting on the water-conducting efficiency of the wood in 
shrubs and trees, Professor Farmer has shown that not only are there great 
differences in the water-carrying powers of deciduous and evergreen trees 
and shrubs, but there may be also variation among the stems and branches 
of the same species when taken from plants growing under different 
conditions and in different localities. 1 
The term ‘specific conductivity 5 is used to express the volume of 
water transmitted by a segment of stem, 15 cm. in length, per 1 sq. cm. of 
wood as seen in transverse section. This volume, given in cubic centimetres 
for the period of 15 minutes, varied for 28 holly twigs from 6-8 up to 12 *2, 
with an average of 8*7 : for Rhododendron ponticum it varied for 50 stems 
from 10 to 25 for the majority, though a few were much lower than 10 and 
a few much higher than 25. It is stated that, in spite of its evergreen 
habit, such variation is to be expected in a plant which is so freely branched 
and has so wide differences in the development of its branches that they 
vary almost from abortion to great luxuriance. . 
Rhododendron ponticum. 
General Morphology . Rhododendron ponticum , L., is a native of the 
Caucasus, but is cultivated in the open air in England and on the Continent, 
and develops well under suitable soil conditions. In a sandy soil the young 
plants will make shoots of 50 cm. in length during one season, but after- 
wards growth is slower, and older bushes rarely make annual shoots above 
1 J. B. F aimer : on the Quantitative Differences in the water-conductivity of the Wood in 
Trees and Shrubs, Parts I and II. Proc. Rog. Soc., B., vol. xc, 1918. 
[Annals of Botany, Vol.XXXIV. No. CXXXVI. October, 1920.I 
