53 



Presumably here, as in Pilea (see Jost, Plant Physiology, 

 English Edit., 1907, p. 425), osmotic pressure tears an anther 

 loose from the base of the stamen, the filament straightening 

 with sufficient force to throw out the pollen. The staminate 

 flowers are in a rather compact catkin and it is likely that the 

 jar of one stamen straightening and bursting is enough to set off 

 the other flowers; at any rate, examination of a catkin after 

 an explosion shows generally that all of the flowers have been 

 sprung and the pollen thrown out. 



Carnegie Museum, 

 Pittsburg, Pa. 



O. E. Jennings 

 \ 



REVIEWS 



Knowlton's Mesozoic and Cenozoic Plants of America* 



Those who have had occasion to deal with American Cretaceous 

 or Tertiary plants have long used and valued Dr. Knowlton's 

 Catalogue published in 1898, which brought together the scat- 

 tered records in the most convenient form. The new Catalogue, a 

 work of 815 pages, enumerates all the Mesozoic and Cenozoic 

 species, including, as Dr. Knowlton informs me, no less than 

 4,789 accepted forms. The fossil plants of Greenland and 

 Mexico are excluded, but those of Alaska are fully cited. In its 

 form and arrangement the new Catalogue resembles the old, 

 but it differs in having a series of extremely useful appendices. 

 The first of these gives the classification of all the genera in 

 orders, families, etc.; the second an index of genera and families 

 in the classification; the third enumerates the plants of each for- 

 mation, from the Triassic to the Pleistocene. The amount of 

 labor represented is enormous, but the saving to others is much 

 greater. My annotated copy of the old list, and my imperfect 

 attempts to cover the ground represented by the appendices, 

 look rather pathetic by the side of this vastly more complete 

 and satisfactory work. We can only hope that with this new 

 aid the very small band of American paleobotanists will be 



* Knowlton, F. H., A Catalogue of the Mesozoic and Cenozoic Plants of North 

 America, U. S. Geological Survey, Bulletin 696, 1919 (published early in 1920; re- 

 ceived at Boulder, Feb. i8). 



