278 REVIEWS. 



extinct, the two extreme forms have survived. The likeness 

 of these two trees is explained by their genealogy, their 

 marked difference by the extinction of the connecting forms 

 which in earlier times bridge the interval. 



SERENO WATSON ON NORTH AMERICAN LILIACE^E.^ 



Mr. Watson, in preparing the Monocotylcdonecc for the 

 " Botany of California," came upon the order LiUacecv, which 

 is well represented in Pacific North America ; and he had 

 to consider how the genera and higher groups should be dis- 

 posed. This led to a wide study of the order and a strict 

 scrutiny of the American species ; and the present " Revision 

 of the North American Liliacese," occupying the greater part 

 of the " Contribution " before us, is the result. It is gen- 

 erally agreed that this order is to have the wide extension 

 which was given to it by the present writer a dozen and more 

 years ago ; and the proper collocation of its diversified forms, 

 with interlaced affinities, has been a problem of no small diffi- 

 culty. Mr. Baker, in England, has attempted the task for the 

 order generally, and has sedulously elaborated some of the 

 North American, but more of the Old World and the South 

 American, genera and tribes. His arrangement and his sys- 

 tematic views are in many respects satisfactory, in some un- 

 satisfactory as respects North American botany. Mr. Watson 

 has the latter primarily in view, but still has to adjust the 

 American genera into the general system. The arrangement 

 be has planned consists of three series, the first of which parts 

 into two subseries, and includes sixteen tribes, some of them 

 divided into subtribes. The great endeavor has evidently 

 been to make natural groups — and this endeavor has been 

 really successful. The next thing is to assign characters, and 

 here comes the difficulty. Absolute chai'acters of the lead- 



^ Contributions to American Botany, IX. By Sereno Watson ; Proc. 

 American Academy of Arts and Sciences. Boston, 1879. (American 

 Journal of Science and Arts, 3 scr., xviii. 313.) 



