DE VRIES'S THEORY OF MUTATIONS. 213 



De Vries has started from the phenomenon above mentioned, so 

 well known to nursery-gardeners and which is often of considerable 

 financial importance to them; the phenomenon that suddenly in some 

 of their flower-beds single variations appear which are constant when 

 reproduced by seed. By systematically propagating these exceptional 

 specimens a quantity of seed may be obtained in a few years that can 

 be brought into the market. Soon, however, the variety loses its mer- 

 cantile value; seed may now be obtained by anybody in increased 

 quantities from the plants that have already been sold. 



Are there any of our native species of plants in which the same 

 phenomenon produces itself naturally ? was the question which de Vries 

 set himself. And if so, can they teach anything about the formation 

 of species? In commencing the inquiry he started with about a hun- 

 dred different species. Of all these, only one exhibited the property 

 sought for — this, however, in such a way as to throw full light on the 

 subject in most unexpected directions. 



The species of plant which de Vries actually managed to detect in 

 the act of 'mutation' on certain fields in Graveland, and which has 

 continued to do so with perfect distinctness during many years in the 

 Amsterdam Botanical Garden, bears the name of Oenothera Lamarchi- 

 ana. It is one of three species of the genus that have been brought 

 over from the United States and is now running wild in Europe. 



De Vries has thus convinced himself that the great majority of 

 plants about us do not show cases of 'chance variations,' 'mutation 

 variation' per saltum; in other words, that the species that have been 

 observed for many centuries may be said to be stable, invariable. But 

 they are stable in so far only as — perhaps with very long pauses — 

 periods of mutability appear, during which, next to the stable central 

 species, new sub-species appear that are also stable when propagated 

 by seed. Further experiments, however, are required to throw light 

 on the periodicity. 



Another conclusion was this, that the species which do produce 

 mutations bring forth not a single mutation, but quite a number of 

 them, varying among themselves. The mutations occur both in plants 

 growing in the wild state and in those samples of (Enothera Lamarcki- 

 ana that are bred under supervision. Their frequency, as determined 

 by exact statistical tables drawn up by de Vries, varies between one 

 and two per cent. Of the 50,000 (Enothera which de Vries has ob- 

 served during ten years' culture, there were 800 that could not be 

 designated by the name (Enothera Lamarckiana. 



A somewhat skeptically disposed person may claim that this num- 

 ber of 800 indicates the number of the most marked deviations which 

 were noticed among 50,000 plants; that, in other words, they are indi- 

 vidual, fluctuating variations that would also be found in the same 



