The Microscope. 91 



more widely scattered than is that of most other microscopical 

 subjects, and the work of collating it is enormously increased by 

 the obscurity of many of the journals in which the original de- 

 scriptions were published, to say nothing of their rarity, their 

 cost and the difficulty of obtaining them ; yet Mr Wolle ha& 

 overcome all these obstacles, and has here given drawings of 

 every form known to exist in North America. The labor ha& 

 been great, but the result is a monograph that no microscopical 

 student can afford to ignore. Even for those that " potter about 

 on the edges of things " it will be an incentive and a valuable- 

 aid to work. To be able to identify those Diatoms with which 

 every drop of ditch water is loaded that comes to the microscope 

 stage, will be a comfort and a delight ; and the possibility of 

 finding this help, with an illustration and references to the litera- 

 ture of the subject included within a single volume, must act as 

 a stimulus to further investigation. Not only are American Di- 

 atomists under obligations to the author, but the amateurs that 

 have hitherto seen the plants and passed them by because of the 

 difficulty of identifying and of studying them, will owe him a 

 debt of gratitude. The monograph should arouse wide spread 

 interest in the beautiful objects, and no reader of The Micro- 

 scope that feels the slighest inclination to study them or even to 

 ascertain only their names, should fail to own the book. The 

 edition is limited to four hundred copies. The anther should 

 have no difficuly in disposing of them, especially at the price. 



By the use of analytical keys Mr Wolle leads the microscopist 

 through the tribes and families to the genera, after which, ta 

 learn the species, it is expected that he will compare his specimen 

 with the illustrations, and as every known North American form 

 is figured, there need be little trouble in this part of the study.. 

 For those that are not experts in the identification of the Diato- 

 macea3, Mr Wolle has smoothed the path in a way that will be- 

 exceedingly encouraging. 



