DEVELOPMENT OF PLANT PHYSIOLOGY 105 



present point of view a chemist, not only discovered oxygen, but was 

 the first to show that this substance is excreted by plants. 



These physicists were the forerunners of Hales and Ingen-Housz, 

 the true founders of plant physiology. Hales, by his studies of sap 

 movement, laid the foundation for physical plant physiology; on 

 the other hand, Ingen-Housz, by his discovery that atmospheric 

 carbon dioxid is dissociated by light in green plants, did the same 

 for the chemical aspect of this study. 



Thus it was that the foundations for plant physiology were laid 

 by the physicists. The next advance, the firm establishment of the 

 discovery of Ingen-Housz, came through Th. de Saussure, who was, 

 in the language of his colleagues, as well as in our own, a chemist. 

 At the beginning of the eighteenth century there was no relation 

 between plant physiology and botany. The botanists, who were 

 of the stamp of the Linnaean School, were completely engrossed 

 in description, and were quite indifferent to the knowledge of the 

 life of the plant, alread}' well advanced. 



The French were the first to show the relation between plant physi- 

 ology and botany. The great botanist, Augustine Pyrame de Can- 

 dolle, came under the influence of his elder colleague and countryman, 

 Th. de Saussure. The great significance of plant physiology, which 

 was at that time too closely identified with physics and chemistry, 

 could not have escaped his far-seeing eye, and he hoped to bring the 

 young science into new life by pressing into service the knowledge 

 of the botanist. In addition to his fundamental studies in systematic 

 botany, he was active as an experimenter in the field of physiology; 

 and by means of his Physiologie vegetale furthered greatly the know- 

 ledge of the life processes in plants by his regard for morphological 

 relations, by the assembling of rich materials for observation, and, 

 in general, by the bringing together of botanical (as then understood) 

 and experimental evidence. 



To the French belongs the credit of having preserved intact the 

 continuity of plant physiology, which was effected, in addition to 

 De Candolle, by the important physiological research of his colleague, 

 Dutrochet, and by others, until Boussingault, whose activity extends 

 into the period of the general dissemination of plant physiology. 



More slowly was the union of this study with botany accomplished 

 upon German soil. The bridge which led from the one to the other 

 was plant anatomy, which, however, shared the fate of plant physi- 

 ology, in being regarded as something strange within the bounds of 

 the older botany. This is explained, of course, by the fact that plant 

 anatomy did not originate with the botanist. 



Plant anatomy was first made possible by the invention of the 

 microscope; in fact, it was this invention which gave the spur to this 

 study. The earliest anatomical observations of plants were made by 



