RECENT ADVANCES IN SCIENCE 383 



study of annual rings, it may be possible to map out districts 

 according to the favourability of their climate for tree growth. 

 For this purpose the author proposes to employ the difference 

 between each two successive rings divided by their mean 

 (mean sensitivity). Trunks of Sequoia gigantea are now known 

 the annual rings of which take us back to 1305 b.c, so that a 

 period of over 3,000 years is thus available for study. 



Economic. — In a valuable paper by H. B. Sifton {Am. Jour. 

 Bot.), the results are reported of an investigation of the ger- 

 minative capacity of some hundreds of samples of common crop 

 seeds which were tested annually over a period of twenty years. 

 Spring Wheat apparently retains its germinative capacity 

 almost unimpaired for the first five years, with but slight decrease 

 up to the tenth year. Between eleven and fifteen years more 

 than 75 per cent, of the seeds die, but a few were still viable at 

 seventeen years. 



Out of a total of 179 samples of Oats, the majority showed a 

 slightly increased germinative capacity after five to six years' 

 storage, and lost their viability much more slowly, nineteen- 

 year-old seeds still exhibiting a germinative capacity of 41 

 per cent. Timothy-grass seed deteriorates rapidly, especially 

 after the seventh year, whilst both Alsike and Red Clover show 

 a regular decline from the first year, which offers a marked 

 contrast to the almost abrupt depreciation exhibited in the 

 other seeds tested. 



PLANT PHYSIOLOGY. By Prof. Walter Stiles, M.A., University 

 College, Reading (Plant Physiology Committee). 



Permeability. — Since this subject was last dealt with in these 

 pages (Science Progress, 12, 575-80, 191 8) it has continued 

 to form the subject of much investigation. Foremost among 

 recent researches on the permeability of plant tissues must be 

 reckoned those of K. Hofler, the results of whose investigations 

 are recorded in a series of papers the first of which appeared 

 towards the end of 191 7. In this first contribution ("Die 

 plasmolitisch-volumetrische Methode und ihre Anwendbarkeit 

 zur Messung des osmotischen Wertes lebender Pflanzenzellen," 

 Ber. deut. bot. Ges. 35, 706-26, 191 7) a new method for deter- 

 mining the osmotic concentration of plant cells is described. 

 The basis of the method is as follows. A cell is plasmolysed in 

 a decidedly hypertonic solution, as a result of which its volume 

 when plasmolysis is complete is reduced by a certain amount, 

 say by ijn of the original internal volume of the cell. If the 

 latter is completely semi-permeable to the plasmolysing sub- 

 stance, the concentration of the cell sap must have increased 

 to njn — i of its original value, assuming that in the original 

 condition the cell was not stretched on account of turgor 



