i9io] DeVRIES— OENOTHERA RUBRINERVIS 3 



hybrids, since both the constituents are available in pure condition 

 for controlling crosses. Any cross which gives twins with rubri- 

 nervis may be repeated with O. deserens and with my O. mut. 

 velutina (O. hlandina). In the first case the result must be 

 hybrids of the type laeta, in the second case hybrids of the form 

 velutina, and the addition of these must simply duplicate the 

 split progeny of the corresponding cross of O. rubrinervis. I have 

 made these crosses in a number of cases and found this deduction 

 verified. 



Apart from the described secondary mutability into viable 

 deserens and dead velutina germs, O. rubrinervis is not known to 

 possess any noticeable degree of mutabiUty; it has, especially, 

 never produced those mutants which are of so common occurrence 

 in allied mutating forms. Thus we see that secondary mutability 

 is not, in itself, to be considered as a cause of further mutations, and 

 this seems to me to be a fact of paramount interest in the discussion 

 concerning the probable causes of this phenomenon. 



The details of the following experiments will give proof of the 

 proposed conception. I shall first give those relating to self- 

 fertilizations and afterward deal with the crosses. 



Oenothera rubrinervis originated in my garden from 0. Lamarcki- 

 ana quite regularly in a percentage of about o. i. Every time the 

 visible characters were exactly the same. Between 1890 and 1900 

 the mutation was repeated 66 times among 66,000 plants.^ In 1905 

 I introduced new rosettes of O. Lamarckiana from the original 

 locality near Hilversum into my garden, and among their offspring 

 I observed also repeated mutations into rubrinervis. The charac- 

 ters were always the same, namely, a pale reddish tinge, narrow 

 and longitudinally folded leaves, a hairy epidermis, cup-shaped 

 flowers, but above all the brittleness of the stems, branches, and 

 petioles, due to the incomplete development of the cell walls in the 

 fibers of the bark and wood. Until now I cultivated mainly two 

 strains, derived from two different mutants of 1895. One of them 

 has given the material for all my crosses, and I shall designate it as 

 the main line. The second line of 1895 was originally destined for 

 control experiments only, but in 1 913 it produced the first observed 



^The mutation theory, English ed. 1:331. 1909. 



