Carbon Dioxide in Maturation, etc., of Seeds. 



623 



appear to be important factors in obtaining the necessary adjustments to 

 natural conditions. 



Emphasis may properly be laid on the fact that it is these adjustments of 

 the moist seed when in apparently suitable conditions of temperature, 

 moisture, and oxygen supply, while awaiting the fit time for germination, 

 and not so much the adjustments of the resting dry seed, that have formed the 

 central problem of seed life in conditions of nature. The maintenance of 

 latency when the moist seed is in conditions of medium temperature, 

 oxygen supply, and moisture, has been the problem of the maturing seed 

 on the parent plant. It has been the problem of a large proportion of 

 native seeds which fall upon the ground in summer and autumn, but whose 

 fit time for germination does not arrive till the following spring. It has, 

 beyond doubt, been the problem also of many species of plants in the struggle 

 for existence whose chances therein must have often been increased many- 

 fold by the capacity of their seeds to lie dormant in the ground for indefinite 

 periods, ready to resume activity with sporadic germination when suitable 

 conditions arise such as, for instance, occurred in the case of the Brassica alba 

 seeds of these experiments when the testas became dry or ruptured. 



Section VII. — Summary and Conclusions. 



Part I. — Experiments were conducted showing that the germination of 

 seeds is retarded or inhibited by high partial pressures of C0 2 in the 

 atmosphere. This retardation and inhibition produced by C0 2 was shown 

 to be unaccompanied by injury. The seeds used in these experiments fall 

 into two classes. In the first class the seeds germinated at once after 

 removal from the inhibitory C0 2 pressures (beans, cabbage, barley, peas, 

 onions). In the second class the inhibition continued indefinitely after the 

 removal of the inhibitory C0 2 pressures, and is terminated only by complete 

 drying (and rewetting), or by the removal of the testa. In this class a 

 lowering of the permeability of the testa to gases under the influence of C0 2 

 is indicated, a change which would have two results : (1) a reduction in the 

 amount of oxygen reaching the embryo ; and (2) a relative rise in the actual 

 C0 2 pressure in the embryo tissues. The condition of prolonged inhibition 

 after removal to air produced in Brassica alba is strikingly suggestive of the 

 condition of seeds often met with in nature, the germination of which is 

 delayed in spite of suitable conditions of temperature and water. The results 

 obtained in the laboratory with Brassica alba seeds were reproduced in the 

 soil in natural conditions by C0 2 arising from decaying vegetable matter. 

 The high C0 2 content of the soil air in these experiments was found to 



