502 A History of Botany, 1860-1900 



such affirmations rested. We may instance Naegeli's theory 

 of growth by intussusception based upon his hypothesis of 

 the micellar constitution of all organized structures, which 

 was not only accepted as demonstrated for starch grains and 

 cell walls, but was by many held to be applicable to the 

 living substance itself. There was a little later Boussin- 

 gault's statement that carbon dioxide is absorbed by the 

 cell wall of the epidermis, and does not enter the plant 

 through the stomata ; similarly there was a general 

 acceptance of Sachs' view that starch is the culmination 

 of the early photosynthetic processes. Indeed throughout 

 the history of the science, repeated instances of the undue 

 weight attached to the dicta of particular workers meet us 

 at almost every turn. The advance that began in those 

 early years was an important one in the direction of freedom 

 of thought. There was a revolt against authority as such, 

 and the statements of the older writers not only ceased 

 to bind the opinions of the younger men, but actually 

 challenged criticism and investigation. The time of specula- 

 tion and hypothesis passed away and the new era of philo- 

 sophical inquiry and rigid experimentation took its place. 

 Not that either speculation or hypothesis failed to take 

 a place in investigation and research, but they lost their 

 dominance ; they were put forward not as final explana- 

 tions of events and circumstances not fully understood, 

 but as suggestions which were to be rigidly examined and 

 discussed, which were indeed only meant to be the basis 

 of experiment and research. 



The effect of this spirit of free inquiry has appeared 

 over and over again in these pages ; the old inexactitude 

 gradually vanished, and the researches of the later years 

 of the century yielded knowledge which was at once farther 

 reaching and based upon more satisfactory foundations. 



Allusion has already been made to the great develop- 

 ment of the biological sciences during the period which has 



