Trelease — Botany During the 19th Century. 127 



species than that marking the immediately preceding decades, 

 because of the geographic exploration already referred to, 

 and still more because of a growing change in the scale of 

 specific differentials which has resulted in the segregation of 

 many forms which under the older views passed for at the 

 most varieties of polymorphic or variable species. The 

 genera Rubus and Hieracium, in Europe, and Viola, Sisyrin- 

 chium and Crataegus, in our own country, well illustrate my 

 meaning. 



Just as the descriptive manuals of Linnaeus, and the editions 

 of them published after his death by Schultz, Willdenow and 

 others, facilitated and stimulated the accumulation of hith- 

 erto unrecognized species at the beginning of the century, 

 its progress throughout has been recorded and accelerated by 

 the publication of later works of the same general character 

 and purpose. For the flowering plants, some of the most 

 noteworthy of such general descriptive works are the incom- 

 plete Prodromus and Monographiae of the De Candolles, the 

 numerous revisions of genera and families in Engler's Jahr- 

 bucher and the Journal of the Linnean Society, and the com- 

 prehensive Index Kewensis prepared by Mr. Jackson under a 

 provision made in Darwin's will ; and no account of this 

 aspect of the science would be at all complete without refer- 

 ence to the books and journals devoted to the illustration of 

 plants, foremost among which stands the Botanical Maga- 

 zine, which, founded by Curtis in 1790, has been continued 

 without interruption, and at the end of 1900 contained 7751 

 colored plates, mostly illustrative of plants of decorative 

 value. For Pteridophytes, the manuals of Hooker and Baker 

 have been most helpful. Bride), Schimper and Warnstorf 

 stand out prominent among those who have published compre- 

 hensive manuals of the Bryophytes, while the enormous 

 Sylloge Fungorum of Saccardo and the as yet incomplete 

 Sylloge Algarum of DeToni have made accessible the myriads 

 of scattered descriptions of species belonging to these groups 

 of the lower cryptogams. 



SYSTEMS OF CLASSIFICATION. 



The simplicity of Linnaeus' s classification of flowerino- 

 plants has been mentioned. The popular handbooks even of 



