210 SECTIONAL ADDRESSES, 
The work of the Darwins, Sachs and Pfeffer on irritability was con- 
tinued throughout this period and, indeed, to the present day. The use 
of Fitting’s intermittent klinostat made possible a quantitative analysis of 
reactions, especially of geotropism and phototropism, and there emerged 
clear conceptions of presentation, excitation, reaction and relaxation 
times. Concurrently, the search for the seats of perception went on; 
the problem was the subject of much experimentation and considerable 
discussion, ultimately general agreement—our present opinions—was 
reached. 
The natural sequence of this tropistic work was an enquiry into the 
mechanism of the sense organ. The radial pressure theory of geotropism 
was mooted and not denied, but it was hardly favoured possibly because 
it is intractable to experimental proof. The statolith theory, due to 
Haberlandt and Némec, proved more attractive and, after many observa- 
tions and much discussion, was, in general, accepted. In addition to those 
mentioned, Noll, Czapek, Jost, Vochting, Oltmanns, de Vries and Rothert 
contributed much to the elucidation of the problems. There remained 
the question of the transmission of the stimulus from the perceptive 
organ to the motive region. Boysen-Jensen (1910) repeated some 
experiments by Rothert on the transmission of stimuli when the veins in 
the coleoptile of Avena were severed. Boysen-Jensen obtained some 
discordant results which, on analysis, showed that a stimulus could pass 
through a water gap but not through a thin plate of mica. Thus arose 
the idea that definite bodies, hormones, were generated in the perceptive 
region by the action of the external agents and travelled to the motive 
organs to activate the visible reaction. These observations were con- 
firmed by Purdie and others and the usual ‘gold rush’ happened. 
Boysen-Jensen continued his work, and amongst those who contributed 
were Nielson, Paal, Stark, Dreschel, Snow, and especially Went. Mention 
also must be made of the work of Ricca (1916) on the transmission of the 
hormone in Mimosa; his work was carried forward by Snow and Ball who 
showed that there is a high speed as well as a low speed conduction. 
Details of this and cognate investigations are omitted; they are the 
theme of our current lectures. It remains to be remarked that that 
brilliant man, Errera, was the first to postulate the action of hormones in 
regulating the growth and development in the plant. 
THE PRESENT. 
The period. beginning in 1919 is an history of our own times, and need 
not long detain us; indeed, the progress in some branches has already 
been alluded to. The rate of advance in morphology and anatomy is 
perforce slower for the obvious reason that with continued activity, new 
material becomes less and opportunities fewer. Kidston and Lang’s 
discovery of and work on Rhynia, Hornea and Asteroxylon was a note- 
worthy advance and in anatomy the investigations on the cambium, 
especially those of Bailey, are of particular merit. The period is chiefly 
remarkable for the great output of work in those branches of botany which 
have an applied aspect. Thus mycology, plant pathology, genetics and 
cytology occupy a prominent position. In physiology but little progress 
has been made in the elucidation of the serial events of the various 
——— 
FE a 
