^jti.Kn9jniy. .',^UWADA.-3IAI0SIS IN THE P, M.C OF ZEA MAYS L. 169 



i6ff tlie'/a.J)QTtive -pollen grains o£.Houttuynm cordata (6). The 

 Jiomotype jor second divisiou does not take place in most cases, 

 and bdth cHrotnosome groups, enter directly into the resting 

 condition (Text-fig. 2) each to forni a nucleus which sometimes 

 shows a sign of amitosis, a phenomenon also reported in 

 Houttuynia cordata. Amitosis in the homotype as well as in 

 the heterotype division is mentioned by Tischler (9) also in 

 ^yringa chinensis, a steril hybrid. In the daughter cell result- 

 ing from the division of such constriction of the cell wall two 

 ■^liuclei come sometimes in view (Text— fig. 3), where they are 

 almost in contact with each other. This must indicate that a 

 second division of nucleus took place. The comparison of size 

 of nuclei in both cases, i.e. the case where the second division 

 took place and the case where it did not, is of an interest. In 

 the latter case they are always larger than in the former. 

 This is an indication that the transverse separation of chromo- 

 somes in the heterotype division represents the second division. 

 R. R. Gates (1) has mentioned in the development of the pollen 

 mother cell of Oenothera gigas that in the anaphase of the 

 heterotype division '' there are indications that in certain cases 

 the second division may be transverse." In my case it seems 

 to me that this transverse separation actually takes place 

 (Fig. 18). 



Though the segregation of chromosomes into two groups is 

 mostly regular and two daughter nuclei are usually formed, 

 there are often found the cases where the chromosomes are 

 irregularly- distributed between two poles, and the result is the 

 formation of several small nuclei and few isolated chromo- 

 somes in the cytoplasm (Text-fig. 4). 



The aforementioned abnormal case does not occur in all 

 pollen sacs of a flower, but only in some of them. It has not 

 been ascertained whether such abnormal pollen mother cells 

 will produce mature pollen grains or not ; but the fact was 

 observed that at the pollination time certain amounts of small 

 abortive pollen grains were usually found mixed with normal 

 grains (Fig. 34). 



Those flowers in which the abnormities were found 



