198 Alfred J. Ewavt : 



tion of the first 3 seeds is .above 22 deg. C, which would explain 

 Nobbe and Hanlein's results with these seeds. The seeds of 

 Hawthorn are supposed not to germinate until after a year in the 

 soil. Crocker obtained no definite confirmation or negation of 

 this faict, but here also it appears to be a case of the slow dis- 

 integration of the seed coats. 



The. Condition of Resting Seeds. — The old idea that the conir 

 l>lete suppression of eveiry form of vital activity necessarily in- 

 volved irrevocable death, led to the assumption that in resting 

 seeds respiration continued, though at a very low ebb. Jodiii^ 

 showed, however, that 20 peas containing as much as 11 per cent, 

 of water, and linseed containing 12 per cent., produced a mere 

 trace of carBon dioxide in four years. Kolkwitz'^ has recently 

 shown in the case of Barley how rapidly the amnunt produced 

 decreases as the percentage of moisture decreasies. 



Barley. — 



Weight of seed. Temperature. Percentage of water. ^^- Produced 



" ' '^ per 24 hours. 



1 Kilogram - Summer - 19-20 p. c. - 3.59 mg. 



- 14-15 „ - 1.4 „ 



- „ - 10-12 „ - .35 „ 



50 deg. C. - 10-12 „ - 15.0 „ 



Becquerel' finds that air-dried seeds give off small traces of 

 carbon dioxide, and a.bsorb traces of oxygen. Exposure to light 

 increases this action, and the gaseous exchanges from the integu- 

 ments of Ricinus are greater than from the seed from which 

 they have been removed. Obviously here we are dealing with 

 extraneous chemical oxidations not connected with vitality. In 

 fact, the drier the seed the less the ''respiration," and in seeds 

 capable of withstanding extreme desiccation the absence of 

 moisture entirely pref\'ents all gaseous exchansfes. A priori this 

 must be the case in all dry seeds covered with a continuous im- 

 permeable cuticular layer. Thus no percejitible evolution of 

 carbon dioxide could be detected from clean dry samples of 

 Acacia seed containing less than 5 to 8 per cent, of water 



1 Ooiiipt. rend. d. I'Acad. des Sciences, t. 122, )>. 134!t, ISDO. 

 •2 Bcr. d. D Bot. Oes., 1001, vol. .\ix., p. 285. 

 3 Comiitcs rcnd\is, t. cxliii., IDOG, p. 974. 



