Alternating Annual and Biennial Habit. 293 



cultivated and have nevertheless not been extirpated. 



The general opinion of botanists is that the represen- 

 tatives of the main line of the evolution of plants have 

 been for the most part perennials. From these the an- 

 nual and biennial forms must have arisen independently 

 in the various families and groups; and it is furtlicr 

 natural to suppose that the biennials arose first and that 

 the annuals arose from them. If this is true the pro- 

 duction of a biennial from an annual or of a perennial 

 by one of these two would have to be regarded as a 

 phenomenon of reversion.^ Instances of such atavism 

 seem to occur very generally in the vegetable kingdom, 

 but progressive transitions, that is to say, those that take 

 place in the opposite direction, are also by no means 

 rare.- 



From the abundant literature on this point I select 

 two cases which seem to me the most important. Pha- 

 seoliis rmiltiflonis {Ph. coecinens L.) is, with us, an 

 annual plant, producing occasionally, however, a bulbous 

 root which can be wintered and by means of which the 

 plant can be perpetuated. Von Wettstein/^ to whom 

 ^we owe our knowledge of this phenomenon, has obtained 

 plants which lived four years, and in my own experi- 

 mental garden I have succeeded in wintering several 

 such Phaseohts tubers. Von Wettstein's view is that 

 we are dealing here with the transformation of a peren- 



^ Many, however, hold the opposite view. See Darwin, Varia- 

 tions, II, p. 5; and Rimpau^ loc. cit. 



' See the works relating to this snhject by Irmtsch and Warming. 

 Also HiLDEBRAND in Engler's Botan. Jahrb., IT, 1882, pp. 51-135; 

 with regard to different sorts of beets: F. SciiiNnLER in Bof. Ccntral- 

 blatt, 1891, Nos. 14 and 15, and the literature cited there. 



^ R. VON Wettstein, Die InnovationsvcrJiiiltnissc von Phascolus 

 coecinens L. (=: Ph. multiflorus IVilld.), Oesterr. hot. Zeitschrift. 

 1897, No. 12, 1898, No. I. 



