6 4 o SCIENCE PROGRESS 



the stipules frequently show indications of a double structure 

 with two midribs or a bifid apex. Such cases may be taken 

 as reversions to the ancestral condition of the Rubiaceae as a 

 whole, in which there were probably two true leaves and four 

 stipules at each node. 



Heredity. — De Vries, to whom we owe so much regarding 

 our knowledge of mutation, has recently described (Bot. Gaz. 

 1916) four mutants of Oenothera in which at every generation 

 the offspring produced are of two kinds in almost equal 

 numbers. Those belonging to the one group resemble the 

 parent, whilst the remainder are typical (Enothera Lamar ckiana, 

 thus reverting to the original stock from which the mutants 

 sprang. From the results of crossing experiments it appears 

 that the characters of these " dimorphic " mutants are only 

 carried by the ovules and not by the pollen . Thus one of them 

 (O. carta), when fertilised by pollen of 0. Lamarckiana, yielded 

 nearly equal proportions of the two types, whilst when the 

 latter was fertilised by pollen of O. cana 98 per cent, were 

 typical Lamarckiana whilst the remaining 2 per cent, were 

 mutants of the nanella type. 



Ecology and Physiology. — An extremely valuable contribu- 

 tion to our knowledge of osmotic pressure as influenced by the 

 environment has been made by V. Iljiu, P. Nazarova, and M. 

 Ostrovskaja (Journ. of Ecology, vol. iv. pp. 160-73, l 9 l &)- 



The subject-matter of their account is based upon estima- 

 tions of the osmotic pressure in the roots and leaves of species 

 growing in different habitats, viz. steppe, meadow and swamp. 

 The average rate of evaporation in the three conditions was 

 approximately in the ratios o*8 : 2*2 : 3*4. The moisture in 

 the soil was similarly least in the steppe, whilst the swamp 

 exhibited permanent saturation. The roots of various species 

 from the three habitats showed a striking correspondence with 

 the humidity of the environment. Roots of plants from the 

 steppe gave osmotic pressures of from 0*4 — 0*48 (normal Na 

 CI soln.), from the meadow 0*19 — 0*3, and from the swamp 

 o* 1 3 — o* 2 . Comparable results were obtained where the same 

 species was taken from different habitats and moreover, even 

 in the same habitat and with the same species, the osmotic 

 pressure showed a decrease when the water content of the 

 soil attained a maximum owing to heavy rainfall. Determina- 

 tions of the osmotic pressure of the leaves likewise yielded a 



