124 Physiologie. 



Um den Säuregrad der Wurzeln zu bestimmen, müsste man eigent- 

 lich nur die VVurzelhaare der Prüfung unterziehen, was aber sehr 

 schwer angeht. — Verf. brachte verschiedene Pflanzen in Lösungen 

 von Natriumnitrit von 0,1 "^„1 wobei sich ergab: Die Kulturpflanzen 

 gingen bald ein, also ein entgegengesetztes Verhalten wie oben. 

 Um einen direkten Anhaltspunkt über den Zusammenhang von 

 Säuregehalt und dem Grade der Nitritgiftwirkung zu erhalten, 

 wurden Lupinenpflanzen 20 Tage in einer 0,01 °'o'gen zitronensäure- 

 haltigen Nährlösung belassen, dann nach Waschen der Wurzel in 

 Natriumnitritlösung von 0,1 "/q. Die Pflanzen starben in 2 Wochen 

 ab, während die Kontrollpflanzen, die aus der blossen Nährlösung 

 in die Nitritlösung versetzt wurden, noch am Leben waren. 



Matouschek (Wien). 



Croeker, W. and W. E. Davis. Delayed germination in 

 seed of Alisma Plantago. (Botanical Gazette. LVIII. p. 285— 32L 

 1914.) 



The writers summarize their researches at the end of this 

 paper as follows: 



Dormancy in the akenes of Alisma plantago is due to the 

 mechanical restraint of the seed coat. This restraint enables the 

 seed to be in water for years without germination. 



The chaffy carpel wall pla3's no part in the dormanc}'. Of the 

 three layers of the seed coat (the outer Single layer of reddish-brown 

 cells, the inner Single la3^er of white cells, and the lining acellular 

 pectic hemicellulose material), the outer seems to plaj^ no part in 

 ■the dela^^ The effect must be attributed to one or both of the 

 inner la3"ers. 



As the intact fruit lies in water in the satured condition, the 

 embryo itself does not half Cprobabl}' not more than one-fourth or 

 one-fifth) consummate its possible imbibitional and osmotic swelling. 

 The embr^'o onh" partlj^ swollen thus lies for years in water, 

 restrained in its swelling b}' the seed coat, against which it must 

 be exerting a pressure of approximatelj' 100 atmospheres. 



The air-dr}^ seed (freed from the carpel wall) when placed in 

 water swells rapidl^'. It increases 40 per cent of its air-dr^' weight 

 in the course of two hours. From this time on it shows a slow 

 increase to 50 per cent of its air-dr}' -weight, which is maintained 

 constant even after long periods of soaking. A large part of the 

 water absorption is due to the h\'drophi]ous pectic and hemicellulose 

 substances of the seed coat, especialh' the inner acellular laj^er. 



When the coat cap is removed from the large end of the 

 embrj'o, thus leaving the embr^-o more free to ccntinue its imbi- 

 bitional and osmotic swelling, the seed swell even much more 

 rapidly, reaching about 60 per cent of its air-dry weight in two 

 hours and more than 100 per cent after 20 hours. The imbibitional 

 and osmotic swelling graduall}' passes into growth enlargement. 



With the coat cap removed from both ends of the embryo 

 and the seed placed in water, the embr^'o elongates 19 per cent 

 of its air-dry length in 2.5 hours. This would extend the embryo 

 at least 20 per cent the length of the swollen seed beyond the 

 limits of the seed coats. This elongation is all imbibitional and 

 osmotic, involving no growth. Five hours' soaking gives an elongation 

 of 30 per cent oif the air-dr}' length of the embryo. This is onl^^ in 

 ver}?- small part due to growth. Sixteen hours' soaking gives 36 



