235 BOTANICAL GAZETTE - [uarcu 
themselves show occasional mutations, and in many cases the same species 
has arisen from different parents. There follow theoretical considerations — 
which may be omitted here, except to state that De Vries believes in periodic 
mutability, since most species now appear to be immutable. What causes 
mutability can only be conjectured; perhaps it is favored by generations of ~ 
excellent nutrition, perhaps by alternations of diverse conditions. oe 
About half of the first volume deals more indirectly with mutation. One 
section treats of nutrition and selection, another with the origin of garden 
varieties, the author finding general agreement in a number of cases ith bis 
work on Oenothera. eee 
Independently and all but simultaneously with De Vries, Korschinsky* 
has brought together a vast mass of data under the title Heterogenesis and ce 
Evolution. From the records of gardeners and horticulturists, he has 
attempted to show that most of the culture “varieties” have arisen throu 
heterogenesis and not by means of selection. Such evidence is not very 
trustworthy in special cases, but perhaps the mass of detail by its mere 
_ quantity may help to strengthen the case as a whole. In any event 
evidence and the fact that it is brought forward independently gives SU 
: to the work of De Vries. Solms-Laubach? has presented evidence: © 
that Capsel/a Heegeri has arisen as a sport from C. Bursa-pastoris. 
