Lutz, Triploid Mutants in Oenothera. 40! 



ularly shaped; at other times a small extra nucleus with a single 

 chromosome, or two small extra nuclei, each containing two chromo- 

 somes, etc. 



It would be very instructive to know whether such irregularities 

 may be found at this stage in the female germ cells of 0. lata, 

 or whether this phenomenon is connected especially with the 

 sterility of the male. 



Irregularities at this stage were occasionally found in the male germ 

 cells of other forms, but apparently in no such abundance as in 0. lata. 

 For example, Gates recorded one case in 0. rubrinervis (11, p. 18) 

 in which two small nuclei were present in addition to the four 

 larger ones composing the tetrad. He also mentions and figures 

 a case in the telophase of the homotypic mitosis of a 21-chromo- 

 some plant (13, p. 188) in which one chromosome was left behind 

 in the cytoplasm. 



These conditions recorded by Gates are very suggestive of 

 irregularities in the homotypic division in certain cases, and are of 

 especial interest, taken in connection with Davis' statement in 

 regard to 0. Lamarckiana (4, p. 952): 



"Th;s, during the homotypic mitosis it is not uncommon to 

 find the. i some of the chromosomes in a group of seven have failed 

 to reach the poles of the spindle, and as a result form smaller 

 supernumerary nuclei in the pollen mother-cell. Such a case is 

 shown in PI. LXXII, Fig. 44, where the chromosomes of three 

 groups, a total of twenty-one, are distributed among five nuclei. 

 Tetrads may even be formed in which large and small nuclei become 

 associated in the same cell and pass into a resting condition, but 

 it is not known whether such a cell can nature into a fertile pollen- 

 grain." 



It is very probable indeed that some of these various aspects 

 observed at the end of the homotypic mitosis are the result of 

 irregularities of the last division. The case recorded by Gates in 

 which one chromosome was found to have been left behind in the 

 cytoplasm after the formation of the daughter nuclei in the telophase 

 of the homotypic division of a 21 -chromosome plant strongly indi- 

 cates that it may be possible for a male germ cell to be finally 

 equipped ivith less than the normal number of chromosomes, though 

 fully supplied at reduction. The question remaining is whether germ 

 cells are functional when supplied with less than the normal number 

 of chromosomes. 



Davis (3, p. 638) reported having observed two cases in 

 O. biennis, and recently (4, p. 949) a single case in 0. Lamarckiana 

 'that showed numerical irregularities in the distribution of the 

 chromosomes by the heterotypic mitosis'. He also refers to but 

 one chromosome passing to the wrong pole of the spindle in these 

 XXXII. 26 



