Igt1] CURRENT LITERATURE AIL 
tion of the fibers. The major ‘part of this abnormal structure forms lignified 
cells with slightly thickened walls. In the case of T. ‘ences ~ ring of vascular 
bundles presents enough resistance to prevent the] yp phy of the medullary 
Tays. However, A. algeriense has a stronger influence on the intermediate 
woody vessels, stopping pin development and causing a hypertrophy of the 
thickened angles of the stem. The vascular bundles in the stem of P. fobira 
are much less resistant than in any of the preceding host plants; in this case 
the insect affects the bark, easily gains entrance to the medullary rays, and 
causes a hypertrophy which results in the separation of the vascular bundles. 
The modification of the tissues between the bundles is advantageous to the 
insect. In the petioles and midribs, the bundles do not form a complete ring 
and therefore are much less resistant than in the twigs, and are subject to much 
greater hypertrophy. In all cases, except the last, the external tissues of the 
stem undergo excessive hypertrophy and form the greater part of the gall. 
The biology of galls is ably discussed by Dr. ARTUR Mopry,” who gives a 
review of the subject and also the results of his own investigations. though 
the study of galls is very old, it has attracted comparatively little attention 
from: biologists. The workers on this subject have defined galls differently, 
but the definition given by BEYERINCK is most generally aie at the present 
time. According to this definition, the gall is a “new formative — within 
the body of the plant and is due to insects or plant organisms.’ MAS 
Suggested the use of the word “cecidien” (meaning nut gall) as a substitute 
for all other terms; then subdivided the galls on basis of cause into Phyto- 
cecidien and Tao cocidiats and these groups sais myco-, . ae phytopto-, 
entomo-cecidien, etc. Although this marked an advance in the study of 
cecidology, it was of very little botanical importance. This w was largely over- 
come by KERNER,* who suggested the following divisions: 
felt 
simple mantle ck 
covering 
solid 
Galls 
foliage 
bud flower 
compound 
others 
This division has been of great value for descriptions. In 1904 Ross sug- 
8ested division into root, stem, leaf, and blossom galls. This division has 
been of considerable value, but was not very practical. LacazE-DUTHIERS 
(1849-1853) suggested division into internal, external, and mixed galls. How- 
ever, the greatest advance was made by KtsTER, who as a result of his study 
relent 
Mopry, Dr. Artur, Beitrige zur Gallenbiologie. 
K. K. Staats-Realschule. 1911. 
*3 KERNER AND OLIVER, The natural history of plants 2:514-554. 1895. 
Sechzigsten Jahresb. 
