Influence of Carbon Dioxide in Maturation, etc., of Seeds. 409 



toxic action of products of oxidation, as its life can be prolonged in the 

 absence of oxygen. 



Again, it has been a feature of recent work under many aspects to 

 emphasise the action of the ordinary metabolic products of cell life in 

 producing deep functional changes, both normal and abnormal. The nature 

 of the action of these products is being studied in detail, and it has 

 become clear in certain cases that what appears to be an act of excitatory 

 stimulus producing a certain forward change is in reality the removal 

 of a depressant stimulus normally present which acts as an inhibitant. 

 Thus, for example, it has been recently shown* that the growth of the 

 mammary glands in a pregnant female is due to a product of foetal growth 

 which acts by overcoming the inhibitory action of a substance which is 

 normally present and prevents the development of these parts. 



The case of antithrombin normally present in the blood in sufficient 

 quantities to inhibit the action of any thrombin ferment formed, and so 

 preventiog any intervascular clotting, is well known. The study of 

 immunity affords a very large number of instances of antibodies whose 

 function is the inhibition of the harmful stimulation of poisons. Czapek (3) 

 in his work on the anti-ferment reaction in tropistic movements of plants 

 has added another interesting example in this line of discovery. He 

 demonstrates geotropic stimulation to be accompanied by an accumulation of 

 homogentisinic acid due to the action of an antiferment inhibiting its break- 

 down by oxydase normally present. 



In this paper the indicated problem of the dormancy of moist seeds has 

 been attacked from the point of view that dormancy must be conditioned by 

 the absence of an essential stimulus or by the presence of an inhibitory 

 agent. The two-sided question therefore which is presented at the 

 outset is as follows : What is the nature of the positive stimulus to 

 germination or what is the nature of the inhibition which must be over- 

 come to initiate this process ? 



Influence of Carbon Dioxide in Inhibiting the Germination of Moist Seeds. 



(a) Carbon Dioxide Inhibits the Germination of Seeds without Producing 

 Injury. — It will be useful to begin with a brief examination of the group of 

 phenomena classed under the term " delayed germination." In one class of 

 eases it is known that many seeds do not immediately germinate in nature 

 even when to all appearance placed in optimum germinating conditions. This 

 is true of a number of native species which remain in the ground during the 

 winter, although freely germinating in the following spring. In another 

 * By Prof. Starling and Miss E. Lane-Claypon (2). 



2 I 2 



