AGRICtJLTURAL BOTANY. 531 



the absolute ash became greater. In the lots without silica the plants con- 

 tained greater amounts of lime, phosphoric acid, and iron in proportion to 

 potash. 



Without afiirming that it is necessary to plants, the author believes that 

 silica has an important biological function in stimulating plants to greater 

 growth, and that it probably plays the role of maintaining a physiological 

 equilibrium in the nutritive solutions in the soil. 



A bibliography is appended. 



The oxyg'en minim.um and the germination of Xanthium seeds, C. A. 

 Shull {Hot. Gaz., 52 (1911), No. 6, pp. 7/53-'/ 77, fig. i).— Attention is called to 

 the fact that while there have been many studies on delayed germination, little 

 has been done toward solving the problems presented by this phenomenon. 



During the past 2 years the author carried on investigations on the rela- 

 tion of oxygen pressure to the germination of Xanthium seeds. He found that 

 the naked embryos of the dimorphic seeds of Xanthium exhibit a marked diffei*- 

 ence in their demand for oxygen for germination, the minimum for the ger- 

 mination of the decorticated upper seeds at a temperature of 21° 0. being 

 approximately 12 mm., while for the lower it was about 9.5 mm. Increasing 

 the temperature 10° lowers the minima to 7 and 3 mm., respectively. The 

 variation of the total atmospheric pressure was found not to influence the 

 oxygen minimum for germination. The author found that there was very little 

 after-ripening, or at least that the after-ripening was not visible in an altered 

 germination behavior at atmospheric pressure and ordinary temperatures. 

 There is evidence, however, of a decrease in the oxygen requirement or an 

 increase in permeability of the coats to oxygen as ripening progresses. There 

 is said to be a slow progressive deterioration of the seeds, which after a few 

 years entirely lose their power to germinate. 



The general conclusion that the organs of the seeds of higher plants can grow 

 in entire absence of free oxygen is not supported by the results obtained. On 

 the other hand, it appears that they can not grow without comparatively large 

 amounts of oxygen. The oxygen pressure required for the germination of the 

 coeklebur seeds was found to be much higher than that reported by Lehmann 

 for sunflowers, zinnias, Glyceria fluitans, etc. 



The high oxygen demand, and the difference in this demand in the two 

 seeds, act with the coats to secure delay and a difference in delay, in the ger- 

 mination of the two seeds. 



The origin of osmotic effects. — IV, Note on the differential septa in plants 

 with reference to the translocation of nutritive materials, H. E. and E. F. 

 Armstrong (Proc. Roy. 8oc. [London], Ser. B, 84 (1911), No. B 571, pp. 226- 

 229). — In a previous paper (E. S. K., 25, p. 26) the authors call attention to 

 the osmotic phenomena in plants which are correlated with effects produced 

 by substances to which they have extended the term hormone. Subsequent 

 studies have shown that the osmotic effects conditioned by hormones indicate 

 that the translocation of nutritive materials takes place periodically. 



The authors' observations show that the outer differential septa in plants 

 are permeable only by substances of a particular type, apparently those having 

 but slight affinity for water. If this is true, other substances such as sugars, 

 for example, can not pass through the septa unless in some measure they are 

 broken down. Studies of Saxifraga sarmeniosa indicate that the cells generally 

 are lined with a septum which is differentially permeable, and it is supposed 

 that the difference in osmotic tension is conditioned by the differential permea- 

 bility of this thin protoplasmic membrane. 



Experiments are cited in which the authors studied the special effect pro- 

 duced by hydrocyanic acid in relation to hydrolysis. If the hormone used is 



