RECENT ADVANCES IN SCIENCE 35 



tissues of the embryo or an insufficient supply of oxygen for 

 germination ; (5) the necessity of the embryo itself to undergo 

 certain after-ripening processes before germination and growth 

 under ordinary germinating conditions are possible ; or, lastly 

 (6) the induction by various means of a condition of dormancy 

 in seeds previously capable of immediate germination. To this 

 special form of dormancy Crocker has applied the term " second- 

 ary dormancy." This author has also emphasised the fact that 

 problems in dormancy lend themselves well to mechanistic 

 attack. 



According to Rose (" After-ripening and Germination of 

 Seeds of Tilia, Sambucus, and Rubus," Bot. Gaz., Ixvii, 1919, 

 p. 281) freshly harvested seeds of Tilia americana with a 

 moisture-content of 10 per cent, or less, or seeds kept in warm 

 storage for several months fail to germinate when placed on a 

 moist substratum at ordinary room temperatures. He has 

 shown by numerous experiments that the germination of the 

 seeds of this plant can be brought about by a period of after- 

 ripening in moist storage at 0° — 2° C. followed by a sojourn of 

 2-3 weeks at io°-i2° C, until germination is well under way. 

 To obtain vigorous growth of the young seedlings a still higher 

 temperature is essential. During the process of after-ripening 

 the hydrogen-ion concentration of the seeds increases, as do 

 also the oxidase and catalase activities. 



Freshly harvested seeds of Smnbucus canadensis similarly fail 

 to germinate when sown at room temperature ; it was found, 

 however, that such seeds, after having been kept in moist soil 

 out of doors during the winter, showed a high percentage of 

 germination ; but the author was unable to determine whether 

 this result was due to the low temperatures obtaining during 

 the winter months, as previously suggested by Kinzel (" Frost 

 und Licht als beeinfliissende Krafte bei der Samenkeimung," 

 Stuttgart, 191 3), to certain constituents of the soil, or to a 

 combination of these or other factors. In the case of Rubus 

 Idcens Rose found that the dormancy of the seeds was prob- 

 ably due to the high breaking strength of the endocarp. Ger- 

 mination of the seeds of this plant was unaffected by light or 

 by darkness. 



Kidd and West (" The Controlling Influence of Carbon 

 Dioxide. IV. On the Production of Secondary Dormancy 

 in Seeds of Brassica alba, following Treatment wdth Carbon 

 Dioxide, and the Relation of this Phenomenon to the Question 

 of StimuH in Growth Processes," Ann. of Bot., xxxi, 191 7, p. 

 457) have shown that germination of White Mustard seeds, 

 sown in the presence of carbon-dioxide under certain condi- 

 tions, can be completely inhibited, and that this inhibition of 

 germination is often maintained for long periods (twelve 



