Physiologie. 187 



Wachstum nichts mit Nutation zu tun hat, dass auch kein Verlust 

 der geotropischen Perzeptions- oder Reaktionsfähigkeit vorliegt, 

 sondern dass die Einwirkung des Aethylens eine reine Umstimmung 

 des Geotropismus herbeiführt; die Stengel verhalten sich nicht mehr 

 negativ geotropisch, sondern wie radiäre transversal-geotropische 

 Organe. Durch Ueberführung in reine Luft wird der normale Geo- 

 tropismus wieder hergestellt. 



Der Grad der Verunreinigung der Luft mit Aethylen kommt in 

 folgenden Abstufungen zum Ausdruck: 1) die Keimlinge sterben 

 ab; 2) sie bleiben am Leben, wachsen aber nicht mehr und schwel- 

 len stark an; 3) sie wachsen langsam, sind verdickt und werden 

 transversal geotropisch; 4) sie wachsen schneller, sind kaum verdickt, 

 und ebenfalls transversal geotropisch; 5) wie vorige, aber schräg 

 nach oben(!) wachsend; 6) sie wachsen normal aufwärts, aber immer 

 noch nur etwa ein Drittel so rasch als in reiner Luft. 



Hugo Fischer. 



Overton, J. B., Studies on the relation ofthe living cells 

 to transpiration and sap-flow in Cyperus I. IL (Bot. Gaz. 

 LI. p. 28-63. fig. 1. 102—117, fig. 1-2. Jan., Feb. 1911.) 



After an historical discussion and an account of some prelimi- 

 nary experiments, detailed experiments with heat and poisons are 

 described. The results are as follows: 



1. Sterns of Cyperus cut and placed in water wither sooner than 

 when a certain portion, not to exceed 20 cm., has been killed by 

 steam. 



2. When 20 cm. of the stem are killed by steam, the leaves 

 wither in about 8 days, that is, in about the same time as the con- 

 trol plants. 



3. The longer the portion of the stem killed with steam, the 

 sooner the leaves above wither and dry. When 25 to 30 cm. of the 

 stem are killed with steam, the leaves wither in 3 — 5 days. 



4. No matter how long the section killed may be, the leaves 

 on steamed stems never wither quite so quickly as those cut and not 

 placed in water, but under the same conditions of light, tempera- 

 ture and air mosture. 



5. In Cyperus sufificient water to maintain the leaves turgid for 

 3—10 days will rise through a stem 15 — 60 cm. high, with a section 

 5 — 30 cm. long which has been killed with steam. 



6. A certain amount of water is raised in the steamed portion, 

 but it gradually diminishes in quantity from day to day until the 

 leaves become air dry (about 1 1 per cent of their dry weight of 

 moisture). 



7. The diminished water supply is partly due to partial blocking 

 of the vessels with a gumlike or resinous substance, which probably 

 owes its origin to the disorganization of the contents of the sieve 

 tubes caused by beating the stems. 



8. The withering of the leaves about a steamed portion of the 

 stem is probably caused more by the action of deleterious substan- 

 ces introduced into them from the dead cells than from lack of 

 water. These poisonous substances are probably disorganization pro- 

 ducts caused by heating with steam. 



9. The leaves of rooted plants grown in nutrient Solutions con- 

 taining sterilized. decoctions of the same plant, droop in 3 — 5 days, 

 discolor and dry in 7—8 days. 



