Physiologie. 253 



cell saps and the freezin^ points ofleaves. (Missouri Bot. 

 Garden. XXIII. Ann. Rept. p. l01-131. PI. 6. 1912) 



The author's conclusions are based upon two series of investi- 

 gations: one, the observations of the effect of a freeze on many 

 trees and shrubs; the other, the artilicial freezing of the leaf saps 

 of the above trees and shrubs. The first is more or less arbitrary, 

 being based mostly on external appearances; the second is h\^po- 

 thetically accurate. From a comparison of these two sets of data we 

 are led to the following conclusions: 



1. That extreme differences in sap density, in general, are 

 accompanied by a corresponding difference in their resistance to 

 freezing. 



2. That exceptions to this general rule are probably due to dilTe- 

 rences of cell structure; and other causes that may enter in, as 

 protective location, etc. 



3. That where cell structure is the same, the densities of the cell 

 saps indicate their relative hardiness, as in the magnolias. 



4. That in plants of the same genus, or varieties of the same 

 species, differences in sap density correspond to differences in their 

 resistance to freezing. Jongmans. 



Osterhout, W. J. V., Plants which require sodium. (Bot. 

 Gazette. LIV. p. 532—536. 2 Fig. 1912.) 



It has long been customary to regard sodium as necessary for 

 animals but not for plants. In the light of our present knowledge 

 of the role of inorganic salts, it is clear that distinction between 

 plants and animals is of fundamental importance, if it be true in 

 all cases; but if exceptions occur, its significance largely disappears. 

 The experiments, described in this paper, were undertaken in order 

 to learn whether there are cases in which sodium is as necessary 

 for plants as for animals, 



One flowering plant was studied, and several genera of algae, 

 among which were representatives of the green, brown, and red 

 algae. The investigation included species from the Atlantic and 

 from the Pacific. 



Sodium is as necessary for the marine plants studied as for 

 animals; its replacement in sea wäter by NH^, Ca, Mg, K, Ba, Sr, 

 Cs, Rb, or Li is decidedly injurious. 



The best Substitutes for Na are the other kations which predo- 

 minate in the sea water. Mg, Ca, and K. 



The behavior of various species toward certain salt indicates 

 that each of these salts has a specific action on life processes, 



Jongmans. 



Rigg, G. B., The effect of some Puget Sound Bog \vaters 

 on the root hairs of J/'a^^sc««//«. (Bot. Gazette. LV. p. 314— 326. 



1913.) 



The theory advanced in this paper is that plants other than bog 

 xerophytes are excluded from peat bogs because of their inability 

 to produce normal root hairs in the toxic habitat of the bogs, their 

 absorptive surface being thus so increased that they cannot get 

 water enough to enable them to live. The experiments were made 

 with Tradescantia. The expression „normal root hairs" means such 

 root hairs as grow on the roots of cuttings in tap water. 



