less fusion, the multipolar structure Ikhouics a bipolar spindle 

 (multipolar polyarch) scnorall) jusl |)rc\i('us lo the jK'riod of 

 metaphase. The formation ot cell jdat^^ s and the disappearance 

 of the spindle fibers have l)een discussed in Section II under the 

 title "Cleava^^e by cell plates." 



Mention should be made of some irrei;ularities in the division 

 and distribution of the chromosomes that are conspicuous in cer- 

 tain spore mother-cells and which have been the cause of much 

 discussion. The subject has especial reference to certain older 

 views of the reduction phenomena in jilants. Chromosomes split 

 once louf^itudinally in all typical mitoses an.d the halves are drawn 

 apart in a synnnetrical manner which is \ cr>' easily understood. 

 This division is really determined by the hni-itudinal fission of 

 the spirem thread. hut appearances durin^L;- the first nuclear 

 division in the spore mother-cell of man\- forms ha\e puzzled 

 investigators for many years and have ,<;i\en rise to a inunber 

 of interpretations. It seems to be prett\- clearh- established 

 now that in these types there is a double longitudmai s])littin<;- 

 of the chromosomes at the time of this mitosis. The first di\i- 

 sion takes place durin- prophase and the second follows closely 

 after the first and is generally clearly seen at metai)l)ase or dur- 

 ing anaphase. Therefore the chromatic bodies which appear at 

 the nuclear plate during the first mitosis are in realitv divitled or 

 about to be divided into quarters and they separate after this 

 mitosis as pairs of granddaughter chromosomes instead of simple 

 daughter elements. These pairs are either firmly united at one 

 end into a V or in-egularly drawn out so that the bodies have 

 very unusual and sometimes bizarre forms. Nuclear figures of 

 this irregular appearance were originally described by Flemming 

 for the first mitosis in the spermatocyte of Salamandra and named 

 by him " heterotypic." These in the spore mother-cell of plants 

 are of similar character and the designation heterotypic " has 

 been adopted by botanists for this C(MKlition. The pairs of chro- 

 mosomes that enter the daughter nuclei after the first mitosis 

 fuse end to end to form a spirem thread which breaks up again 

 during the second mitosis, without longitudinal fission, into pairs 

 of chromosomes which are believed to be identical with those 

 that entered the nucleus after the first mitosis. Since there is 



