82 HISTORY OF BOTANY 



employs in all his researches, the logical manner in which 

 he marshals his facts, and the careful deductions he 

 draws from them. Doubtless his mental attitude owed 

 much to his intimate association with his father, the dis- 

 tinguished physicist and Alpine climber, and perhaps even 

 more to his thorough study of the writings of Lavoisier. 

 By many De Saussure is spoken of as the last of the little 

 band of investigators in plant physiology who flourished 

 at the end of the eighteenth and in the very early years 

 of the nineteenth centuries. I think it would be more 

 correct to regard him as the forerunner of the new school 

 of chemical biologists represented more than a generation 

 afterwards by Boussingault and Liebig In any case, in 

 whichever category we elect to place its author, there can 

 be no doubt that in De Saussure's treatise we have a 

 classic well worthy to rank alongside the Vegetable Staticks 

 of Hales and the Experiments on Vegetables of Ingen-Housz. 

 Another outstanding feature in the department of 

 physiology in the early years of the nineteenth century 

 is the work of Thomas Andrew Knight. His earlier 

 investigations dealt with the circulation of sap, but there 

 he was obsessed with the idea that the sap of plants 

 corresponded to the blood, and that therefore there must 

 be a circulation in the plant comparable with that seen 

 in the animal. Notwithstanding Ingen-Housz's work 

 on the subject, Knight still held to the notion that the 

 sap, after having reached the leaves via the vessels of the 

 wood, and after having been exposed there to light and 

 air, acquired, " by means I shall not attempt to decide, 

 the power to generate the-various inflammable substances 

 that are formed in the plant. It appears to be then 

 brought back again through the vessels of the leaf stalk 

 to the bark, and by that to be conveyed to every part 

 of the tree to add new matter, and to compose its various 

 organs for the succeeding season." Knight even went 

 the length of resuscitating the ancient idea that there 

 were valves in the bast vessels for regulating the sap 



