236 PHYSIOLOGY [Box.. Absts, Vol. IV, 



1568. Niexburg, Wilhelm. Uber phototropische Kriimmungen an langsseitig zum Teil 

 verdunkelten Avena-Koleoptilen. [Phototrophic curvature of the coleoptile of Avena which 

 was subjected to partial lateral shading.] Ber. Deutsch. Bot. Ges. 36:491-500. 1919. — Ex- 

 periments carried on with Avena seedlings support the view of Darwin that phototrophic 

 reactions are dependent on sensitiveness to differences of illumination and not on the direc- 

 tion of the light source. In agreement with the observations of Blaauw, the mechanism of the 

 curvature is to be sought in a decreased growth on the side exposed to the light. — Ernst 

 Artsckwager. 



1569. Shtjll, C. A. Orientation of roots. [Rev. of: Holman, Richard M. (1) The ori- 

 entation of primary terrestrial roots with particular reference to the medium in which they are 

 grown. (2) Influence of the medium upon the orientation of secondary terrestrial roots. 

 Amer. Jour. Bot. 3: 274-318, 407^14. 1916.] Bot. Gaz. 67: 376. 1919. 



1570. Stark, P. Das resultanten Gesetz beim Haptotropismus. [The resultant law in 

 haptotropism.] Jahrb. Wiss. Bot. 58: 475-523. 22 fig. 1919. — The experiments were carried 

 on with seedlings of Avena saliva, Hordeum vulgare, and Agrostemma Githago. It was found 

 that in case a single flank was sensitized the degree of response was in direct proportion to the 

 amount of stimulus applied. If two flanks were sensitized equally strong, the curvature was 

 in the direction of the bisector of the angle, but the greater the angle between the two flanks, 

 the less definite was the response and the greater was the deviation from the mean. Increas- 

 ing the size of the angle and at the same time increasing the stimulus resulted in the same 

 percentage of curvature, but the differences in the deviation from the mean remained the 

 same. Keeping the angle between the two flanks constant and increasing the amount of stim- 

 ulus results in an increase in the percentage of curvatures and in a decrease in the deviation 

 from the mean of the bisector of the angle. If the two flanks are unequally stimulated, the 

 angle of curvature will be determined by the parallelogram of forces. The deviation from the 

 mean is usually below the value of 1°, at most 1.9°. The same is true if three or four flanks are 

 sensitized equally or unequally, The deviation from the mean is usually below 1°. However, 

 this does not always hold true. Sometimes it happens that the curvature takes place in the 

 direction of the greater sensitized flank. — E. F. Artsckwager. 



GERMINATION, RENEWAL OF ACTIVITY 



1571. Crocker, William. Secondary dormancy in seeds. [Rev. of: Kidd, F., and C. 

 West. The controlling influence of carbon dioxide. The production of secondary dormancy in 

 seeds of Brassica alva following treatment with carbon dioxide and the relation of this phe- 

 nomenon to the question of stimuli in growth phenomena. Ann. Botany 31: 457-487. 1917.] 

 Bot. Gaz. 67: 269-270. 1919. 



1572. Crocker, William. Light and germination. [Rev. of: Lehmanx, Ernst. Uber 

 die minimal Belichtungszeit welche die Keimung der Samen von Lythrum Salicaria auslost. 

 Ber. Deutsch. Bot. Ges. 36: 157-163. 1918 (See Bot. Absts. 2, Entry 611).] Bot. Gaz. 67: 

 520. 1919. 



1573. King, Charlotte M. "Time and season" among the trees. Rept. Iowa State 

 Hortic. Soc. 53:416-417, 1918. — A brief discussion of rest period and of phemologic data 

 on trees. — L. H. Pammel. 



1574. Rose, R. C. After-ripening and germination of seeds of Tilia, Sambucus and Rubus. 

 Bot. Gaz. 67:281-309. 1919. — Air-dry seeds of Tilia americana, Sambucus canadensis and 

 Rubus Idaeus do not germinate when placed on a moist substratum at room temperature. 

 In no case does water-absorption seem to be the limiting factor. Air-dry seeds planted in 

 the soil over winter gave low percentage of germination. The author states that for Tilia, 

 dormancy is not due to the seed-coats but to an actually dormant endosperm or embryo or 

 both. Seeds after-ripened at temperatures slightly above freezing germinate readily at 10° 



