De Vries : Atavistic Variation in Oenothera 79 



phylogenetically older than the Hnear ones, because they are the 

 rule in the whole genus. But some authors suppose that from 

 time to time there arise exceptions to the ordinary laws governing 

 hybrids, and that such exceptions might be the source of many 

 inconstant varieties and even of inconstancy in general. In this 

 case the chance of getting such an exception by crossing would 

 scarcely be greater than that of getting a mutation from the pure 

 type. 



However slight these chances may be, I propose to try both 

 ways and to see whether it would be possible to repeat the as yet 

 doubtful and unknown original production of my 0. cruciata varia. 

 For there are not a great many cases in which the starting-points 

 are to be had in so pure and so thoroughly controlled a state as 

 in this instance. As to the question of the rule of the constancy 

 of 0. cruciata under cultivation, and of the hybrids, I hope to 

 solve this in some years ; but as to the chances of getting excep- 

 tions, it is evident that these are only small and that it would be 

 preferable if the same experiments were made by a number of in- 

 vestigators. 



The aim of such experiments would be to repeat artificially 

 the production of 0. cruciata varia and by this means to throw 

 some light on its origin in particular and on the origin of incon- 

 stant varieties in general. With a view to the possible repetition 

 of this cross I will now give a description of the inheritance of the 

 broad and linear petals in this variety. In so doing I limit myself 

 to the detailed exposition of a single experiment carried on with 

 the descendants of one original specimen of my variety. 



In the year 1897 this plant was raised from seed obtained in 

 the usual way of exchange between botanical gardens. I obtained 

 but a single specimen, which bore all the characteristics of the 

 typical 0. cruciata. The spike, before the opening of the flowers, 

 was placed in a bag of prepared parchment paper to prevent any 

 visits from bees. The anthers touch the stigmas when opening, 

 and the flowers fertilize themselves without any aid. In the same 

 way I always took care to collect each year purely pollinated 

 seeds only. 



This original plant bore but a few seeds, from which during 

 the next year I obtained only sixteen flowering individuals. But 



