620 Mr. F. Kidd. The Controlling Influence of 



maximum which, at the temperature used, is obtained at about 3 per cent or 

 slightly over, and then declines again through a restraining effect to complete 

 inhibition. 



We appear, therefore, to have in view results confirmatory of the, 

 hypothesis that we are here dealing with the effect on germination and. 

 growth of a true narcotic agent, and that the results induced by C0 2 in the, 

 resting seed are a phase of narcosis. 



Section V. — Influence of C0 2 in Enforcing, Dormancy in Certain Seeds which 

 do not Naturally have a Long Dormant Phase. Seeds of Hevea 

 brasiliensis. 



A considerable amount of work has been done in the past — work which is, 

 well summarised by Becquerel(S) — upon various effects produced in dry 

 seeds by sealing them in various gases and vapours, including C0 2 . Becquerel 

 discounts the value of part of this work on the ground that it has been 

 conducted on seeds with impermeable testas, so that the gases used could not 

 be considered to have reached the plant embryo. 



In a number of experiments conducted during this inquiry on seeds with 

 naturally permeable testas, and on rapidly deteriorating seeds in which the 

 testas may be assumed to be at least partially permeable, carbon dioxide was 

 found in nearly all cases to have certain definite effects, such as might have 

 been expected from the foregoing experiments conducted upon wet seeds in 

 germinating conditions. 



The results of this work, which is still in progress, have not yet been 

 correlated, but one aspect of them may be referred to here, as bearing directly 

 upon the central problem discussed in this paper. 



One of the most rapidly deteriorating seeds is that of Hevea irasiliensis. 

 In planting in the tropics it is found that it is always desirable to put the 

 seed in the ground within a fortnight, and Mr. C. Curtis, late director of the 

 Botanical Gardens, Penang, from whom the seeds used were obtained, writes 

 that even in such circumstances 70 per cent, germination is considered good. 

 This rapid deterioration of the seed has been a difficulty in the recent 

 extension of rubber plantations, and the question of the best conditions for 

 preservation in packing and export has been an important one, leading to 

 practical research. The seeds are at present usually packed in ground 

 charcoal and ashes. Their size is about that of an average acorn or larger. 

 They have easily permeable testas and a high water content, and while living 

 they were found to be respiring very rapidly. They were also found to be 

 very intolerant of drying. The seeds in the experiments considered in this 

 research were enclosed in hermetically sealed flasks under various conditions,, 



