REVIEWS 703 



the top through the operation of surface tension, and forms a bubble, which may 

 afterwards burst spontaneously or be pierced by the uprising central jet. 



If the velocity at contact is still further increased, then, after the basket-splash 

 has closed over the air-tube following in the wake of the sphere, a jet may be 

 projected vertically downwards from the roof of the subsiding splash into the air 

 beneath. 



The forces at work near the surface of the sphere as it enters the liquid are 

 beautifully illustrated by a study of the case in which a falling drop of liquid takes 

 the place of the solid sphere. 



The book can be understood without any previous knowledge of physics : its 

 text consists for the most part of descriptions of the photographs ; but brief 

 explanations of a general kind are given of the way in which the forces at work 

 may produce the observed phenomena. The author thus presents a record, easy 

 to follow and full of interest, of a study in which patience and experimental skill 

 have played a conspicuous part. He adds a new interest to everyday occurrences 

 of which the significance is apt to be overlooked, and supplies the reader with 

 a key to the comprehension of phenomena which must often have seemed 

 mysterious. 



S. W. J. Smith. 



Les Zoocecidies des Plantes d'Europe et du Bassin de la Mediterranee. 

 Tome i. By C. Houard. [Pp. 570, with 824 figures and 2 plates.] 

 (Paris : A. Hermann, 1908.) 



This work will be completed in two tomes, the first of which has now appeared. 

 It will prove to be of great service to the student of vegetal galls and their 

 makers, and also to the economic biologist. 



It is really a catalogue of all the known galls produced by animals, so far 

 ound in Europe and the Mediterranean area. 



As far as we have checked it, it seems to be most complete. In this first 

 tome no fewer than 3,319 galls are enumerated. This number, however, includes 

 many of the same species indexed over and over again on the various host-plants, 

 and does not represent the actual number of distinct species of gall-forming 

 animals. To find the actual number of galls produced by various creatures the 

 reader must count up for himself. We hope a complete list of animals which 

 produce these deformities on plants will be given in Tome ii. 



The gall-formers and their products are mentioned under the names of the 

 various plants upon which they occur. This is an excellent method of treating 

 this subject and will enable the student of economic biology easily to trace down 

 any of these structures on cultivated plants. 



In the present tome the gall-formers on the Thallophytes, Muscineae, and 

 Vascular Cryptogams are all dealt with, and those on the Phanerogams up to the 

 Rosaceae. 



In many of the chief families of plants a short general introductory account, 

 printed in small type, is given of their gall-forming enemies. Then each genus 

 and species is mentioned, and the galls and their originators catalogued under 

 each species of plant. A very brief description of many of the deformities produced 

 is given, and references by number added below in small type — references to 

 bibliography — which will, of course, follow in Tome ii. 



To show the great number of gall-formers by which plants are liable to be attacked 

 we may point out that the author records no fewer than S3 on Coniferae of various 

 kinds, 177 on various Gramineae. The Fagaceae (Chestnut, Beech, and Oak) 



