igoS] CURRENT JJTERATURE 279 



the direct excitation of each stimulus, y the counter-excitation set up thereby, 

 k the increment of y, n any number of additional terms, and c the response. 

 No good reason appears for assuming a counter-reaction. Partial ox complete 

 recovery from the primary excitation in the intervals of stimulation is a simpler 

 assumption and would seem equally to account for the facts. Further details 

 must be sought in the paper itself.— C. R. B. 



Edaphic steppes in Sweden. — The ^'alfvar'' is a name given in Sweden to 

 some remarkable formations that occur chiefly on the island of Oland, and to a 

 lesser degree on the island of Gotland, and in the mainland province of Vestcr- 

 gotland. The name ''alfvar" is applied to extensive treeless plains, whose 

 underlying rock is a Silurian limestone. While there are several plant formations, 

 the alfvar presents general ecological unity, and it has an extremely xerophytic 

 stamp. It is somewhat similar to the ''garigue" of southern Europe, and to 

 certain rock formations of Sen'ia. The physiognomy is that of a steppe, and 

 yet there is anything but a steppe cb'mate in Sweden. There is no question 

 that the alfvar is determined by edaphic causes in the main (such as the dryness 

 and temperature changes of the rocks, which are everywhere at or near the surface, 

 and the poverty of the scanty soil), reinforced by strong insolation and constant 

 winds. The alfvar is very distinct in every way from the heath. Such a region is 

 relatively rich in species, of which more than half are glacial or subglacial, and 

 about a third are representatives of the oak flora. Six per cent, belong to the cli- 

 matic steppe, and only 2 per cent, to the beech forest flora. This flora is doubt- 



less a relict of a much more widespread flora in the. period succeeding glaciation 

 There are two general aspects, the dominant aspect of the steppe, and the lesser 

 aspect of the meadow. The herbaceous plants commonly dominate, although 

 shrubs are frequently conspicuous. The leading character plants of the steppe 

 are Mollia tortuosay Helianthemitm oelandiciim, and Cynanchum vinceioxicum. 

 The chief shrubs are Jimiperus communis and PotentiUa jruficosa. In less xero- 

 phytic places, Fesiiica ovina assumes a prominent place. There are often vast 

 areas of Cynanchum almost alone, giving almost an exact picture of certain 

 climatic steppes. Perhaps the most interesting part of the paper is the discussion 

 of nanism. The author distinguishes facultative dwarfs, due to environmental 

 causes, and constitutional dwarfs. Constitutional dwarfs (the group to which 

 the term nanism more properly applies) differ from facultative dwarfs not only in 

 breeding true, regardless of conditions, but also in a much greater qualitative 

 reduction. Constitutional dwarfs show reduction in all organs, not chiefly m 

 aerial vegetative organs; roots and rhizomes are reduced, while they are rarely 

 reduced and often actuaUy increased in facultative dwarfs. Constitutional dwarfs 

 also show reduced floral organs, their intemodes are fewer as well as shorter, and 

 thek leaves are reduced in number as well as in size. ^lost of the dwarfs are 

 annuals, although some show a certain lability as to their duration. Species 

 commonly perennial or biennial, for example, may become annual in^ verj- dry 

 situations. The usual "protective" structures of xerophytic vegetation occur 



