Physiologie. 663 



rature to growth in plants have obtained widely varying resulls, 

 both as to the position of the optimum temperature and as to the 

 nature of the graphs obtained, led the author to this study of the 

 relations holding between constant temperatures, lengths of exposure 

 periods, and growth rates of Zea Mays seedlings. The latter were 

 grown in the dark, careful attention being paid to keep temperature, 

 humidity, and other conditions constant. The thermostats used were 

 capable of ready change when desired and were so adjusted as to 

 maintain the temperature of the plant Chambers within a ränge of 

 fluctuation of 0.5° C. Measurements of growth increments of the 

 shoots were made hourly in most cases, and Observation was conti- 

 nued for periods ranging in length from 12 to 39 hours. 



The graphs obtained showing the relation between temperature 

 and average hourly growth rate give no indication of a double 

 Optimum temperature for growth, as is shown in Koeppen's earlier 

 curve for maize seedlings. They show a rounded or flattened apex, 

 such as Koeppen's curve would show if conventionalized. The 

 Optimum temperature for a 3-hour period of exposure was found to 

 be 29° C, for 9 and 12 hours of growth, 32° C. 



Van 't Ho ff 's law (that chemical reaction velocity is doubled or 

 trebled b}'- each rise in temperature of 10° C), was found to apply 

 for medium temperatures to the growth process in maize seedlings; 

 within the temperature ränge of 20° to 32° the value of the coeffi- 

 cient varies from 2.40 to 1.88. 



The maximum temperature for growth was found to be 43° C. 

 for an exposure period of 15 hours, while 42° is the corresponding 

 maximum for 18 hours. 



The alteration in the mean hourly growth rate with prolonged 

 exposure to constant temperature is brought out bytables and graphs, 

 The initial rise in this mean rate is very rapid but the curves 

 become less steep as the curve maximum is approached, this maximum 

 being reached in a shorter period with higher temperature. A füll 

 bibliograph}^ is appended. Sam F. Trelease. 



Munoz del Castlllo, J., Einfluss des Thoriums auf das 

 Pflanzen Wachstum. (Internation. agrar.-techn. Rundschau. V. 

 7. p. 944-945. 1914.) 



Versuche mit Gerste wurden im radiologischen Universitäts- 

 Institut von Madrid ausgeführt. Die Samen wurden in 2 mit 

 Erde gefüllte Topfe aus gebranntem Ton eingelegt. In den einen 

 wurde vorher ein wenig Thorium gegeben. Die hier gewonnenen 

 Samen kamen wieder in 2 Töpfe, von denen der eine wieder etwas 

 Thorium erhielt. Die 3. Generation der Gerste, die dem Thorium 

 ausgesetzt war, zeigte eine so starke Entwicklung der Blätter, dass 

 man sie für eine neue Sorte hätte halten können. Das Wachstum 

 wird also gefördert, ja noch mehr als bei Anwendung von Ra- 

 dium, u.zw. auch das Wachstum der Nachzucht. — Es gibt sicher 

 viele Böden, die von Natur aus Thorium-Emanation zeigen; man 

 müsste solche für Saatzucht verwenden. Doch stehen Untersuchun- 

 gen von Böden in dieser Hinsicht noch aus. Matouschek (Wien). 



Shive, J. W. , An improved non-absorbing'porous cup 

 atmometer. (Plant World. XVIII. p. 7—10. f. 1. 1915.) 



Description of a new form of rain-correcting atmometer in which 



