KNOWLEDGE OE THE MUTATING OENOTHEEAS. 55 



Another result whicli has not previously been recorded is as follows : The velutina from 

 e r, of 0. biennis X O. LamarcUana was pollinated by O. Lamarclciana, giving the three 



typ 



d 0. Lamar chiana . This cross when repeated gave the sam 



result, the proportionate numbers being, moreover, about the same in both cases 

 i. €., the velutina were five or six times as numerous as the other types, though the 

 numbers were rather small for determining ratios (see Table VII.). It was hoped that 

 a number of other crosses which I had made would permit a solution of this interesting 

 situation, but many of them failed to develop, so the results are still incomplete. 



With the above should be compared the two cases (Table VII., p. 56) in which the 

 hvbrid O. LamarcJciana X 0. biennis was pollinated by 0. Lamarckimia and yielded a 

 series of rosettes w^hich apparently contained the two types O. laeta and O. Lamarcldana^ 

 thouo-h there is much variability. A further series of crosses will be necessary before this 

 behaviour can be fully understood. According to DeVries (1911) (O. LamarcUana X 

 biennis) X Lamarchiana gives pure Lamarckiana at least as regards rosette characters, 

 for he does not speak specifically of the flowers. It seems questionable whether the 

 latter will not remain intermediate in all these hybrids. If the rosettes from this cross 

 all belong to O. Lamarckiana they show, at least in my cultures, a much greater range 



of fluctuation than pure cultures of that form yield. 



In the important paper above referred to, DeVries describes double reciprocal hybrids 

 between O. biennis and 0. muricata, the results being in agreement witli the predictions, 

 on theoretical grounds, of Giglio-Tos (1908, 1911). Thus (O. biennis X mimcata) X 



(muricata X biennis) gives 0. biennis which remains true, and (O. muricata X biennis) 



muricata) gives 0. muri 



(d) Results. 



^-^ 



It would at first appear, from a survey of all the results of crossing in the 

 Oenothera, that we are dealing with four distinct types of hybrid behaviour: (1) crosses 

 of O. Lamarckiana with its mutants, except O.gigas; (2) crosses oW.gigas with various 

 forms ; (3) crosses between the large-flowered and small-flowered species of Oenothera ; 

 and (4) Mendelian behaviour in occasional characters such as in O. brecistijlis and O. rubri- 

 calyx when crossed with their parents. But I believe it can be showm that types (1) and 

 (3) are essentially the same, and the peculiarities of type (2) in which it differs from the 

 behaviour of the other mutants are, as I have already indicated, probably to be explained 

 in connection with the presence of a double set or tetraploid number of chromosomes, 

 the members of the extra set of chromosomes varying in their distribution in different 



hybrid crosses. 



In the first place, it is possible that the appearance, for example, of O. n 

 and O. Lamarckiana in the F^ of crosses between these forms is only an extreme case 

 corresponding to the laeta and velutina appearing in, e. g., O. biennis X O. LamarcJciana. 

 In both cases, later generations of both types breed true (usually), the difference being 

 that in the former case the types derived from the cross are at least closely similar to, 

 if not identical with, their parents, while laeta and velutina are quite as different from 



b 



