iv PREFACE. 



Gray, who ardently desired that these valuable materials should 

 be used in continuation of the plan begun by the donor, it was 

 arranged that I should undertake the work in connection with 

 Mr. Thomas P. James, of Cambridge, who would make the 

 microscopical analyses of such species as had not yet been 

 satisfactorily examined, and prepare sketches from which 

 descrii^tions could be drawn. 



As large numbers of specimens and even whole collections 

 were sent to us for determination, the work progressed slowly, 

 but it was drawing toward completion when two years ago Mr. 

 James was suddenly called away by death. 



I have since finished the descriptive part of the woi-k, with 

 assistance from Mr. T. Kenauld, an eminent French bryologist, 

 in the examination of some Hypneoe that had not been surely 

 determined. 



But I was prevented by age and sickness from visiting Cam- 

 bridge in order to complete at the library of the Herbarium 

 the bibliographical part of the work, which could not be done 

 with the few books at my disposal. In the emergency, having 

 greatly admired the manner in which Mr. Sereno Watson — 

 not a professed bryologist — had elaborated the Mosses of the 

 Botany of California, I besought his assistance, little compre- 

 hending at the time the weight which I was imposing upon one 

 whose time and energies were already overtasked. This labor 

 of revisal, and the charge of the work in its progress througli the 

 press, Mr. Watson at length consented to undertake, especially 

 through regard to the memory of his friend, my associate, Mr. 

 James. It has involved a large amount of critical and editorial 

 labor, and I dee2:)ly regret that I am permitted to do no more 

 than to acknowledge, as I gratefully do, my profound obliga- 

 tions to him. But I may bespeak the thanks of all those who 

 are to use this volume, which he has made much more valuable 

 and better adapted to their needs than it would otherwise have 

 been. 



