54 THE CANADIAN NATURALIST. [Vol. vii. 



BOTANY AND ZOOLOGY 



Genera Lichenum: An Arrangement of the North 

 American Lichens. By Edward Tuckerman, M.A., Pro- 

 fessor of Botany in Amherst College. Amherst, 1872. — Many 

 of our most industrious botanists have ne2;lected the lower forms 

 of plant life. Possibly this is as much the result of the want 

 of sufficient books of reference and of authentic collections, easily 

 accessible, as of the greater patience and discrimination required 

 in studying the lower organisms. Notably the Lichens have 

 failed to excite enthusiasm : and yet how common and how con- 

 spicuous many of them are ! The bare rock where no other life 

 could thrive is often decked with variously coloured Lichens : 

 on the ground amid the moss and on the old decaying stumps 

 which too often stud the Canadian fields they are met with : our 

 old palings have their coatings of them, dry and crisp ; and 

 parasitic-like they roughen the bark of almost every tree. For- 

 tunately for science in America they have not been altogether 

 overlooked. We have long known that Professor Tuckerman, of 

 Amherst College, has made them a subject of special study, and 

 to him botanists from various parts of North America have sent 

 their collections for determination or criticism. Anything from 

 his pen is sure to evince great care and unsparing labour, and 

 the volume before us, the result of long and patient study of these 

 collections, is no exception. In the preface he in brief tells us 

 that the work is "a final report to the friendly correspondents 

 of the author on the vspecimens which for many years they have 

 sent to him for determination ; and such determination implying 

 a certain arrangement, the book is a further report upon what, 

 after iinich labour, has commended itself to him as the best 

 ascertained systematic disposition of the Lichens." 



The value of spores in the determination of genera and species 

 is now well known, though minor distinctions depending on size, 

 septation, and the number of spores in each spore-case have by 

 some authors been allowed too much weight. Professor Tucker- 

 man's views on this subject, which first appeared in a pamphlet 

 published in 1866, on Lichens of California, Oregon and the 

 Bocky Mountains, are that '' analysis scarcely indicates more 

 than two well defined kinds of Lichen spores, complimented, in 

 the highest tribe only, by a well defined intermediate one. In 

 one of these (typically colourless) the originally simple spore, 



