581.1 382 [June 



II 

 Some Recent Progress in Root-Physiology 



IN the early years of the present century some of the more 

 fundamental questions in the life of the root were for the first 

 time recognised and studied. Through the long tale of years which 

 have since followed, these questions have never been lost sight of ; 

 and now, when we have entered upon the last decade of the 

 century, the same problems are being attacked with unabated vigour. 

 As the facts are slowly gathered in, we view the problems with 

 greater clearness, and ask the questions in new and more philo- 

 sophical forms. Without unduly extending this article with a full 

 account of all the changes and advances which have taken place 

 during the last few years, some of the more recent and more 

 important additions to root-physiology may be briefly examined. 



As is familiar to everyone, a root growing under equable 

 conditions of moisture and the like will extend itself vertically 

 downwards. If it be displaced from its normal position it will 

 slowly curve round until its tip once more regains the vertical. 

 This effect is due, on the one hand, to the force of gravity acting as 

 a stimulus; and, on the other hand, to the inherent property of the 

 living tissues of the root, by virtue of which they respond to such 

 outward influences. The peculiar property of living tissues which 

 enables them to respond to external influences or stimuli, is spoken 

 of as their irritability, and the directive action of gravity upon the 

 growth of plant-organs becomes effectual through that special form 

 of irritability which is called geotropism. 



In the action of any stimulus on a living organ of a plant, 

 two events must be clearly distinguished : the perception of the 

 stimulus, and the reaction to the stimulus. Between these two 

 stages of the phenomenon a third may or may not be interpolated, 

 viz., the conduction of the stimulus. In the animal body we have 

 precisely the same series of events. A certain influence, such as a 

 prick, a cut, or a burn agitates the end-organs of the sensory nerves 

 lying in the skin of one's finger. The reaction, viz., the conscious- 

 ness of pain, takes place in the brain, which is widely removed from 

 the point of perception. Between the two events we have the 

 conduction of the disturbance along the fibres of the nerves which 

 connect the one organ with the other. 



Turning once more to plant roots, it will be seen that it is an 

 interesting question to determine whether or no the perception 



