624 Mr. F. Kidd. The Controlling Influence of 



continue for a considerable period. Attention was called, to the importance 

 of these facts in agriculture. • . 



Part II. — A long series of experiments was carried out to determine the 

 relation of carbon dioxide inhibition in seeds to temperature and to oxygen 

 supply. Low temperatures and low oxygen supply were both found to 

 increase the inhibitory value of given partial pressures of C0 2 , while 

 inversely the inhibitory value of given carbon dioxide pressures diminishes 

 with a rise of temperature and with a rise of oxygen pressure. The 

 probable relation of these facts to the dormancy of the moist seed in natural 

 conditions was pointed out. 



The arrested development of maturing seeds on the plant was shown not 

 to be due to lack of moisture or to any physiological insufficiency. The seeds 

 in this stage were shown to contain in their tissues more CO2 than seeds 

 normally germinating contain at the moment of sprouting. The presence of 

 the testa was shown constantly to retard the germination both in seeds taken 

 from the parent plant before natural drying and in seeds after complete 

 drying and storing. Attention was drawn to the correlation found to exist 

 between the viviparous habit and the absence of seed coats. 



Carbon dioxide has been considered as a narcotic agent. Previous work on 

 the action of CO2 upon growth has been quoted. The stimulatory effect of 

 low partial pressures, rising to a maximum with increasing pressures and then 

 declining to inhibition with higher pressures of C0 2 , has been demonstrated 

 by experiments with Brassica alba and Hordeum vulgare germinated in 

 the dark. 



In the case of certain rapidly deteriorating seeds {Hevea brasiliensis) the 

 carbon dioxide naturally produced by respiration of the seeds in a closed flask 

 rose to 40 per cent, and the presence of this was found to be accompanied by 

 a marked prolongation of vitality in the seeds. This prolonged vitality was 

 far in excess of that reached with the present commercial method of packing 

 these short-lived seeds for export. 



When we correlate the results of these different lines of experiment we 

 seem to get in various directions evidence of the importance of carbon dioxide 

 pressure as a controlling influence in the biology of seeds. This influence 

 may be formulated briefly in the following principles : — 



(1) The resting stage of the moist seed is primarily a phase of narcosis 

 induced by the action of carbon dioxide. 



(2) Both the arrested development in the case of the moist maturing seed 

 on the plant, and the widely occurring phenomenon of delayed germination in 

 the case of the moist resting seed, which does not germinate although in 

 apparently suitable conditions of temperature, moisture, and oxygen supply, 



