BOOKS AND CURRENT LITERATURE 151 



basis. All problems in afforestation and many problems in refor- 

 estation have to be attacked on the basis of the physical conditions of 

 open country rather than on those of a mature forest. Those who 

 have only a text-book acquaintance with climatology, and recall the 

 widely separated isothermal and isoanemic lines of the smoothly con- 

 structed maps, may find it difficult to realize that very considerable 

 and very important differences of climate may exist within a stone's 

 throw of each other on account of topography or dissimilar vegetations. 

 The experienced forester knows that such is the case, and appreciates 

 the value of a knowledge of these differences in handling the forests 

 in such a manner as to secure the optimum reproduction. — Forrest 

 Shreve. 



Rest Period.— The occurrence of a rest period in plants has been 

 the subject of an immense amount of investigation. During this rest 

 period certain physical and chemical changes are continually going 

 on which are essential to the release of the growth processes and to 

 these changes is given the name "after-ripening." A survey of the 

 literature on the underlying causes of this phenomenon reveals the 

 presence of two widely diverse opinions one of which claims that the 

 rest period is a direct response to changing external conditions and 

 the other that, it is the 2'esult of fixed, hereditary, internal causes. From 

 a study of the rest period in potato tubers Appleman 2 has made 

 some important contributions to our knowledge of this subject. He 

 shows that the latter explanation is inadequate in that the rest period 

 may be entirely eliminated. He was able to sprout potatoes at any 

 time by removing the skins and supplying favorable conditions for 

 growth. Sprouting in new potatoes may be stimulated by subdued 

 light or by wrapping them in cotton saturated with hydrogen peroxide 

 which is decomposed by catalase within the tubers. The rest period 

 is therefore to be regarded as correlated with the supply of oxygen 

 to the internal tissues which in nature is regulated by skin characters. 

 That water absorption is not the prime factor is shown since tubers 



2 Appleman, C. O., Study of rest period in potato tubers. Md. Agr. Exp. 

 Sta. Bui. 183: 181-226, figs. 17. 1914. Physiological behavior of enzymes and 

 carbohydrate transformations in after-ripening of the potato tuber. Bot. Gsz. 

 62: 306-315. 1911. Changes in Irish potatoes during storage. Md. Agr. Exp. 

 Sta. Bui. 167: 327-334. 1912. 



