78 



SCIENCE 



[N. S. Vol. LIV. No. 1386 



the University of Pennsylvania. They in- 

 fested fish, turtles, mussels, and snails. One 

 species {Dina fervida) appears to be a scaven- 

 ger only. 



Little attention was given to the worms 

 other than the leeches, and these with the 

 sponges and protozoans are considered in 

 only nine pages. 



About three fifths of the second volume 

 treats of the plants of Lake Maxinkuckee and 

 vicinity, particularly with the aquatic forms. 

 In addition to annotated lists of species there 

 are important general discussions of such sub- 

 jects as the uses of water plants to the other 

 organisms of the lake and of the floral 

 regions; the latter were found to be as fol- 

 lows: Beach; lake plains; low woodland; up- 

 land clay woodland; upland loamy woodland; 

 gullies ; woodland i)onds ; peat bogs ; and shift- 

 ing sand regions. No reference appears to be 

 made to fungi, although it is well known that 

 some forms like Saprolegnia attack fish. 



Throughout the treatment of the plants of 

 the region, there is much on their relation to 

 fish and other life of the lake; and it is noted 

 that: 



While the division line between the lake flora 

 and the land flora is in most cases pretty sharply 

 drawn, it is not easy to tell where the boundary 

 line lies between plants having some influence upon 

 the lake and those which have none, if there be 

 such. 



The grouping of species in the lists of 

 water plants is puzzling and perplexing till 

 one reads the easily overlooked explanation 

 on page 135, where we are informed that fioat- 

 ing plants are first disposed of and then those 

 of the deeper water, proceeding from thenoe 

 to the shallow water. In this arrangement 

 species of a genus and sometimes subspecies 

 of a species are separated. This is likely to 

 be annoying to the taxonomist but not to 

 students! of ecology or plant distribution. 



Only the first volume of the work has 

 illustrations, and nearly all of these are of 

 fish, tliere being a few of frogs, and some gen- 

 eral views loaned by the Culver Military 

 Academy. The latter are not numbered or 

 referred to in the list of illustrations. 



The well-reproduced colored drawings, mostly 

 from Forbes and Eichardson's " Fishes of 

 Illinois," give considerable attractiveness to 

 the publication and also add to its scientific 

 value since the fish are very accurately shovm. 



There is a large folded map in the back of 

 the first volume. This has a scale of 400 feet 

 to the inch and gives bottom contour lines 

 for every difference of ten feet and for the 

 depths 85 and 88 feet, 89 feet being the maxi- 

 mum depth found. 



The books are well printed in a large, clear 

 type on good, heavy paper, and there are very 

 few typographical errors. All through the 

 work is evidence of much painstaking. The 

 binding is in good cloth. "Withal they make 

 an attractive addition to the naturalist's 

 library as well as a useful publication for 

 his reference and study. 



T. L. Hankinson 



The Roosevelt Wild Life 

 Forest Experiment Station, 

 Syracuse, N. Y. 



SPECIAL ARTICLES 



AN EXPLANATION OF LIESEGANG'S RINGS 



Eaphael Ed. Liesegang in 1898 ^ published 

 results showing that when silver nitrate solu- 

 tion is placed on a gelatine gel containing 

 potassium bichromate, there develops on stand- 

 ing a series of concentric precipitations of 

 silver ehromate.^ These zones are known as 

 Liesegang's rings. Wilhelm Ostwald ^ pub- 

 lished an explanation of the formation of 

 these rings which was accepted until Liese- 

 gang,^ Bechold,* and Hatschek ° cited ex- 

 periments which showed it untenable. Ost- 

 wald's explanation is briefly: Under certain 

 conditions supersaturated solutions are 

 formed, and when solid crystals or nuclei 



1 Liesegang, Zeit f. Phys. Chemie, 1907, 59, 444. 



" For details see Ostwald-Fischer, ' ' Theoretical 

 and Applied Colloid Chemistry," Wiley and Sons, 

 New York, 1918. 



3 Ostwald, "Lehrbueh der Allg. Chemie" (2 

 aufl.), XL, 778. 



iBechold, Zeit f. Phys. Chemie, 1905, 52, 185. 



5 Hatschek, E., Kolloid Zeitschrift, 1911, 9, 97; 

 1912, 10, 124. 



