416 Mr. F. Kidd. The Controlling Influence of 



From the above tables of results it is clear that the case of Brassica alba 

 seeds is peculiar in that the inhibition extends after the removal of the 

 inhibiting C0 2 pressures from the atmospheres over the seeds. This after- 

 inhibition may extend for months accompanied by a sporadic germination. 

 The presence and condition of the testa seem to be the controlling factors in 

 this after-inhibition. Germination is at once induced by the removal of the 

 testa or usually by the complete drying of the seed. 



(c) Delayed Germination in Nature.— From these experiments it is clear 

 that a condition is produced in the seeds of white mustard after treatment 

 with increased partial pressures of CO2 which very closely parallels that of 

 seeds showing delayed germination in natural conditions. This fact is 

 brought out more clearly when the results obtained in the laboratory 

 with Brassica alba seeds are compared with the results recorded by Nobbe 

 and Hanlein (6) as occurring in nature. These authors give a large number 

 of cases in which they observed indefinitely delayed germination in natural 

 conditions accompanied by the sporadic sprouting of some of the seeds 

 extending over long periods. A few examples may be given. 



Table VI. — Extract from Nobbe and Hanlein's Tables of Seeds showing 

 Delayed Germination in Natural Conditions. 



Number and name 

 of seeds. 









Germinations after 



- days. 







5 



7 



8 



16 



145 



351 



519 



874 



Finally. 



Capsella bursa-pastoris, 



3 



6 







10 



14 



31 



58 



75 



400 seeds 





















Thlaspi arvense 







1 



3 





5 



15 



37 



87 



A similar result was obtained by these authors with a large number of 

 species. The following may be mentioned : — Chelidonium majus, Myosurus 

 minimus, Plantago media, Potentilla argentea, Veronica beccabunga, Chenopodium 

 album, Campanula, rotundifolia, Campanula persicifolia. 



The similarity shown in the results obtained with the seeds of Brassica 

 alba inhibited under the influence of C0 2 in artificial conditions to those 

 demonstrated by Nobbe and Hanlein (6) as occurring in natural conditions 

 is thus very marked. 



Again, Crocker (5), working on a special case of delayed germination in the 

 upper seed of the burr of Xanthium, which, in contradistinction from the- 

 lower seed of the burr, does not germinate in the first year after ripening but 

 in the second, found that by removing the testa he could induce immediate 



