52 



DE. E. E. GATES — CONTRIBUTION TO A 



In view of the results of Miss Lutz, in wliicli two 0. lata j)lants having 15 chromosomes 



■ 



occurred in the P^ of a cross with 0. gigcf^s, and the result of Geerts's that the chromosome 

 numher in these crosses is 21 in Pj and hecomes 14 in Pg, we may assume that an 

 extrusion of the extra chromosomes from the nuclei has occurred, in some cases during 

 the division of the fertilized e^-g in the original cross, in other cases during the reduction 



divisions in the Pj plants. The former case would be in harmony with certain results of 

 Ealtzer, Herhst, and Tennant in connection with the behaviour of the chromosomes in 

 hybrid Echinoderm larvae, in which the extrusion of certain chromosomes takes place 

 during cleavage. 



This leaves unexplained the result of Miss Lutz in obtaining six pure O. gigas plants 

 having the Qigcis chromosome number, in the Pi of 0. lata X 0. gigas. There is another 

 possible explanation of the two lata plants in the Pi of this cross, namely, that they 

 originated apogamously. I obtained experimental results some time ago (Gates, 1909 b) 

 which showed with a certain degree of probability that a small percentage of the ovules 

 of O. lata ■will develop without fertilization. 



It is clear that further experiments are required before these somewhat conflicting 

 results can be fnlly understood. It is at least evident, however, that 0. gigas diifersfrom 

 the other mutants in giving, in some cases, an Pj which is intermediate between the 

 parents, in other cases two or three different types ; and it appears that the variation in 

 crossing-bchavionr is closely connected with the distribution and fate of the chromosomes 

 in the various hybrids. 



(c) Crosses between O. biennis and O. Laraarckiana and its derivatives. 



These crosses between large-flowered and small-flowered forms display a number of 

 interesting and peculiar features. (1) The reciprocal crosses are not alike, the hybrids 

 being usually distinctly patuoclinous. (2) These hybrid races breed true in later 

 generations, except in certain characters such as dwarfing, in which they split. 

 (3) Certain crosses (chiefly those in which O. Lamarchiana or one of its derivatives is the 

 pollen parent) exhibit two types in the P^ both of which are different from either parent. 

 These DeVries calls twin hybrids. They are respectively broad- and narrow -leaved, and 

 are called laeta and veliitina. The same laeta and velutina types may be derived from 

 several different crosses, or they may differ in certain minor characters according to the 

 parents used. (4) The flowers of these hybrids appear to be in all cases intermediate in 

 character between those of the parents. The flowers are larger than O. biennis, but 

 smaller than O. LamarcMana, and the styles are short enough so tliat the anthers touch 

 the base of the stigma and secure self-fertilization. There is, however, a considerable 

 range of variability in both these features of the hybrid flower. 



DeVries has described this type of hybrid behaviour in several papers (1907, 1908, 

 1909), and Andrews (1910) has added anatomical notes on the structure of the hybrids, 

 but no figures of these hybrids have been published. In a number of crosses which 

 are summarized in Table VII. (p. 5G), I have obtained results wliich are in general 

 agreement with those of DeVries, though certain probably important differences are to be 



