Progress of Botany . 41 



North American Systematic Botany, by issuing as their 

 joint work the " Flora of North America," between 1838 

 and 1843. The publication embraced the Polypetalae and 

 the Gamopetalae, to the end of the Composite ; and it was 

 not till 1878 that the remainder of the Gamopetake was 

 published by Dr. Asa Gray. In 1840 Sir William Hooker 

 cjave to the world his great work, " Flora Boreali Ameri- 

 cana," in which he recorded all the knowledge then reached 

 of the species of our Continent and of their distribution, 

 gathered from early travellers and explorers. 



Up to this period many individuals were at work on 

 the Continent of Europe, in Great Britain and in North 

 America, collecting and classifying species, and numerous 

 publications issued from the press, some of them of a 

 popular description, which created a widespread interest 

 in Botany and disseminated information on the subject. 

 The Hookers, father and son, who were successively 

 superintendents of the Boyal Gardens at Kew, took the 

 lead in this good work in Great Britain, and they were 

 aided by Balfour, Arnott, Babington and Bentham. 



But a new era for the science was at hand, and as a 

 contributory cause to its introduction were the improve- 

 ments made upon the microscope. Difficulty had long 

 been experienced in the use of lenses of great magnifying 

 power, on account of the breaking up of the rays of light 

 into their elementary colors. The invention of achromatic 

 microscopes removed this obstacle. Professor Amici, of 

 Modena, found, in 1812, that by combining concave and 

 convex lenses the colour aberrations could be checked, and 

 since his day improvements have gone on, until now the 

 highest magnifying powers can be used in examining 

 minute objects and yet a true image of them be secured. 



Another factor contributing to the advancement of 

 Botany during the past century ought to be mentioned ; 

 that is the p'olicy of the governments of all civilized 

 countries in : instituting national surveys for the purpose 



