198 Varietäten etc. — Physiologie. 



endemism to the true or herbaceous habit is also considered. 

 The following objections to the „Age and Area" hypothesis 

 are raised: 



a) Many effective factors other than age determine the area 

 occupied by a species, notably physical and climatic barriers, the 

 adaptability of species under different environment, the rapidity 

 with which they may become dispersed, and the growth form to 

 which they belong. 



b) An analysis of various floras shows that the hypothesis 

 necessarily implies that trees and shrubs are producing new species 

 very much faster than are herbs, a conclusion against which there 

 is much evidence. 



c) The fact that herbaceous species have a much wider average 

 ränge than woody ones necessarily implies that the herbaceous 

 dement in the Vegetation of the world is more ancient than the 

 woody element, a conclusion against which there is also much 

 evidence. 



d) „Dying out" of species is apparently taking place in many 

 cases, both by actual extermination, which causes the last survivors 

 to appear as „relict" endemies; and by the „swamping" of isolated 

 members of old species by crossing with newly developed forms. 



Agnes Arber (Cambridge). 



Iljin, V., P. Nazarova and M. Ostrovskaja. Osmotic Pres- 

 sure in Roots and in Leaves in relation to Habitat 

 Moisture. (Jour. Ecol. IV. p. 160—173. 1916.) 



The investigations were made at the Biological Station of the 

 Petrograd Imp. Soc. Nat. Osmotic pressure was determined by 

 plasmolysis in normal NaCl of the cortical parenchyma of the root, 

 and of the epidermis of the leaf. Three types ot Vegetation were 

 examined: 1) grass steppe, somewhat open (Festuca ovina, Stipa 

 capülata, etc.); 2) meadow, a dense and tall herbage of grasses (Poa 

 pratensis, Triticum repens, Phleum, etc.) and dicotyledons {Geranium 

 pratense, Centanrea jacea, etc.); 3) swamp, marginal {Alisma plan- 

 tago, Veronica beccabunga, etc.) and water (Typha latifoliä). Tables 

 are given showing soil moisture and evaporation by atmometers, 

 during August; the latter was greatest on steppe, least in swamp. 

 Osmotic pressure in roots (see Tables) is greater in steppe and 

 least in swamp. In the case of individual species, the osmotic pres- 

 sure varies, it is higher on the dry steppe. The osmotic pressure 

 in the leaves is not so uniform. It bears no direct relation to pres- 

 sure in the roots. Low osmotic pressure identical to that in roots 

 may be found in leaves in a moist environment or deeply immersed 

 in dense surrounding foliage. Tables show that the pressure is 

 higher in the upper leaves of a plant if these are freely exposed 

 above the surrounding foliage, and lower if the lower leaves are 

 deep in the foliage canopy. It majr also vary in the same leaf, e. g. 

 Typha with lower part of leaf in water (023), and apex freely ex- 

 posed (080). So also the osmotic pressure in the same plant reflects 

 climatic variations between drouedit and moistness. W. G. Smith. 



*&>' 



Morosov, V. A., Die Rolle des Kalziums bei der Er- 

 nährung der jungen Zuckererbsentriebe mit Ammo- 

 niaksalzen. (Landwirtschaft!. Institut in Moskau, Arbeiten des 



