1914] CROCKER &* DAVIS— DELAYED GERMINATION 319 



8. There is some evidence that acid increases the imbibitional 

 force of the embryo. If such is the case, the increase is very slight. 

 Bases increase greatly the rate of elongation of embryo. 



9. It seems that the effect of acids and bases on the germina- 

 tion of Alisma seeds is largely to be explained by a weakening of the 

 seed coats, so that the imbibitional and osmotic swelling of the 

 embryo is capable of breaking away the coat cap at the large end 

 of the embryo. It is possible that they are also in part effective 

 by increasing the force of the imbibitional and osmotic swelling. 



10. This gives a chemical-physical explanation which displaces 

 the vague implications of the term "stimulus." 



11. The seeds of Alisma, as of the seeds of water plants in gen- 

 eral, are capable of lying in water for years in the imbibed condition 

 without losing their vitality. In contrast to this, seeds of land 

 plants will withstand such storage for a relatively short time. 



12. The embryo of Alisma, at the expense of its stored foods 

 alone, is capable of more than 120 per cent elongation in total 

 absence of oxygen. For various other phases of its development 

 (greening, branching, development of primary root) it requires 

 some free oxygen. The greening requires at least 5 mm. of air 

 pressure, the branching more than 5 cm. of air pressure, and the 

 general development of primary roots still more. 



University of Chicago 



and 

 Kansas Agricultural College 



LITERATURE CITED 



1. Atwood, W. M., A physiological study of the germination of Avenafatua. 

 Box. Gaz. 57:386-414. 1914. 



2. Becker, Hans, Uber die Keimung verschiedenartiger Friichte und 

 Samen bei derselben Species. Inaug. Diss. Minister, pp. 129. 191 2. 



3- Behrens, J., Uber die Beeinflussung der Keimfahigkeit gewisser Samen 

 durch Xarkose und Verwundung. Ber. Bad. Land. Versuchs-Anstalt., 

 Augustenberg, 60-64. 1906. 



4- Borowikow, G. A., Uber die Ursachen des Wachtums der Pflanzen. 

 Biochem. Zeitschr. 48:230-246. 1913. 



5- Brown, Adrian J., On the existence of a semipermeable membrane 

 enclosing the seeds of some of the Gramineae. Ann. Botany 21 : 79-87. 1907- 



, The selective semipermeability of the covering of seeds of Uordeum 



vulgare. Proc. Roy. Soc. London B 81:82-93. 1909 



