202 SECTIONAL ADDRESSES. 
a sugar-like substance. Baeyer (1870) seized upon this fact, and thus was 
born the well-known hypothesis which is still the theme of so many in- 
vestigations on carbon assimilation. 
Respiration —Before 1831 certain fundamental facts of respiration 
were known: Ingen Housz had shown that the plant absorbed oxygen 
and evolved carbon dioxide and de Saussure had discovered that a con- 
tinuous supply of oxygen was necessary for the life of the ordinary plant, 
that the more vigorous the organ the greater was the amount of oxygen 
consumed, and that this is associated with a rise in temperature. 
Dutrochet (1837) confirmed the work of de Saussure and showed that 
responses to stimulation are not made in the absence of oxygen. He 
understood, as far as was possible at that time, the diffusion of gas into 
and out from the leaf and he appreciated the intercellular space system 
as a physiological structure. Further, he distinguished between the 
evolution of oxygen in carbon assimilation and the evolution of carbon 
dioxide in respiration which facts were confused by many subsequent 
workers ; and although Garreau (1851) continued and amplified Dutrochet’s 
observations especially on the intensity of the respiration of germinating 
seeds and buds, there was much confusion of thought until Sachs cleared 
up the situation in 1865, especially the significance of oxygen and carbon 
dioxide in carbon assimilation and respiration. After this, progress for a 
time was slow, but interest was at last re-awakened ; Detmer published 
his work on the physiology of germination in 1880 and in this year 
appeared the first edition of Pfeffer’s Physiology of Plants. A few years 
later saw the first results of the work of Bonnier and Mangin on the 
respiratory quotient (1884) and of further investigations by Pfeffer. 
The common hypothesis that in respiration there are associated a 
fermentative and an oxidative phase calls Pasteur to mind. He was the 
first to distinguish between wrobic and anerobic plants, and he con- 
tributed most to the scientific foundation of that ancient practice, 
alcoholic fermentation. 
Trritability—aAlthough Knight published his observations on the 
reactions of shoots and roots to the stimuli of gravity and centrifugal 
force in 1806, progress in this branch of botany was sporadic and slow. 
Dutrochet (1837) considered that the intensity of light was all important 
in heliotropic movement whilst Payer and others maintained that the 
quality of light was the significant factor. In 1865 Darwin’s ‘ Movements 
and Habits of Climbing Plants’ appeared. Its subsequent issue in book 
form (1875) roughly coincided with the publication of several important 
contributions on the subject: de Vries on twining plants and tendrils, 
Pfeffer on autogenic movements and especially Sachs on the various 
tropistic movements. Sachs’ invention of the klinostat was a notable 
event and rendered possible an analysis of geo- and heliotropism. Mention 
also may be made of Darwin’s ‘ Power of Movement in Plants’ (1880), 
which was condemned in no uncertain fashion by Sachs, in wh 8 
developed the thesis that circumnutation is the basis from which 
ztiogenic movements have been derived. 
The reasons for our deficiencies in this second epoch are patent. In 
the first place, the classical traditions of our old universities dominated 
PRR ae WES Ete tage eee phd ety 
SPT are & 
