1912] CURRENT LITERATURE 183 
cancerous growths of animals may be due to insects, and that improved tech- 
nique will throw light upon the problem. He expresses regret that the prog- 
ress of this line of work has been so slow, and reviews some of BEIJERINCK’S 
works which he believes have the most important bearing on the subject. He 
believes that the insect (larva) secretes an enzyme which causes a proliferation 
of the body cells without changing their physiological function, and that this 
enzyme can be transferred from cell to cell. The possibility of insects being the 
cause of such growths in animals was taken up in Krebs Institute in Heidelberg 
in connection with the study of an endemic disease of rats. The rats suffered 
from an infectious disease causing papillose tumors, but the technique was not 
satisfactory in demonstrating the exact cause. The author presents a number 
of microphotographs of insects and sections of plant galls, which he discusses 
in relation to their similarity to animal tumors. He also briefly reviews the 
works of several authors who have expressed similar opinions. 
One of the most valuable discussions concerning the character and grouping 
of galls is by Ktster,3 who suggests a division of the galls into two groups, 
“histoide” and ‘“organoide.” The former includes such simple structures as 
cork formed about wounds, and the more complex structures such as oak galls, 
which, although made up of plant tissue, are unlike any of the plant organs. 
The latter includes the formation of roots from a leaf, those modifications of 
stems and leaves which are usually known as teratological structures, and those 
modifications of parts which are due to fungi and insects. The author discusses 
n of the leaves of the willow due to Aphis amenticola, the witches’ 
Seoihas of the cherry, birch, and fir trees due to Exoascus cerasi, E. betulinus, 
and Melampsorella caryophyllacearum, the cone gall of Salix caprea which is 
due to Rhabdophaga rosaria, the leaf modifications of Populus tremula which are 
due to Eriophyes dispar, the formation of new roots on Poa silvestris due 
to Cecidomyia poa, the formation of adventitious parts on Fraxinus ornus 
and Pteris quadriaurita due to Eriophyes fraxini and Taphrina laurencia, as 
illustrating the various types of organoides. This is followed by a brief dis- 
cussion of a number of insect and fungus galls which possess characters of 
both histoides and organoides. The author attaches no importance whatever 
to the cause, but bases his classification entirely on the character of the deform- 
ity without regard to the fungus or insect which produces the stimuli. 
A brief but very interesting paper by Harrist shows that as vague a 
subject as teratology may present problems for serious investigation. His 
greatest variant being less than 1 per cent. Although the author states that 
he considers the number of pods studied entirely too small for satisfactory 
3 Ktster, E., Ueber organoide Misbildungen auf Pflanzen. Aus der Natur. 
7:°673-685. torr. os 
4 Harris, T. Artuur, Teratological fruits of Pelea. Bull. Torr. Bot. Club 
38: 385-387. rorr. 
