Trelease — Botany During the 19th Century. 137 



morphologists and systematists, and, while much remains to 

 be done, its blocking out is likely to stand as one of the more 

 important achievements of the century just closed. 



APPLIED BOTANY. 



Hand in hand with the advance of pure botany, and largely 

 dependent upon it, have gone at least as great advances in the 

 application of ascertained facts; and the best agricultural 

 practice of to-day, as exemplified in the intelligent use of 

 fertilizers, the rotation of crops, etc., is conformed to the 

 teachings of vegetable physiology, while the knowledge of 

 the plasticity of plants has made each of the later decades 

 the recipient of numerous improved races and varieties of 

 cultivated species. To-day, among the more pliable forms, 

 within certain limits that cannot yet be overstepped, new 

 varieties suited to special needs are selected and bred by men 

 like Burbank with surprising rapidity and accuracy, almost 

 to drawing and specification, because of the practical appli- 

 cation of the knowledge that plants are plastic under environ- 

 ment and selection. 



The details of other contributions of botanical science to 

 human needs are of no less interest. Modern brewing is 

 carried on scientifically, as a result of the fermentation studies 

 of Schwann and Pasteur and the cultural investigations of 

 Hansen, a yeast being employed which has developed from 

 a single cell of known pedigree and properties. Citric acid 

 and vinegar are produced with equal certainty if less com- 

 plexity of manipulation, and the method of pure cultures 

 of the necessary ferments is coming into considerable use in 

 the ripening of cream for butter and of cheese. 



Perhaps the most markedly useful application of the botan- 

 ical knowledge of the century is in the field of medicine. In 

 the early part of the century, the physician was of necessity 

 a botanist, and indeed many of the botanists whose names ap- 

 pear in this account were physicians by training. From the 

 Middle Ages he had the knowledge of physic that character- 

 izes primitive man everywhere to-day, and this had gradually 

 come to represent a pseudo-science of therapy which he prac- 

 ticed by diagnosis, prescription and exhibition, — if I may 



