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1899 | STUDIES ON REDUCTION IN PLANTS 9 
together again, the four chromosomes arranging themselves in a 
tetrad, two going to the first polar body and two remaining in 
the egg cell. These two split and form another tetrad, two 
chromosomes going to the second polar body and two remaining 
in the egg nucleus. This brings about reduction in the first 
mitosis. 
Beliaieff? for a number of years has maintained that a reduc- 
ing division takes place in plants, and, based on his studies of the 
division of the pollen mother cells of Iris, classifies the modes 
of division of the nucleus in plants into three types: (1) the 
vegetative division; (2) the heterotypic division; and (3) the 
reducing division. The heterotypic division takes place, as is 
well known, in the first mitosis of the pollen mother cell, and 
the reducing division accompanies the second mitosis. 
Calkins? announces reducing division during the second 
mitosis of the pollen mother cell in Pteris and Adiantum. 
Calkins was unable to determine whether the reducing division 
in Pteris and Adiantum occurred during the primary or secondary 
mitosis, since the tetrads were packed so closely in the nuclear 
plate of the first division. During the secondary mitosis the 
diads elongate to forma rod. This elongation he thinks takes 
place in the direction of the axis of the spirem, and would thus 
show that the primary mitosis is an equation division, while 
reduction takes place during the secondary mitosis. Neverthe- 
less he recognizes that it is immaterial whether reduction takes 
place during the first or second division. The formation of tetrads 
in the prophase of the primary mitosis is generally regarded as the 
preparation of the number of the chromosomes which are to be 
eventually distributed to the four daughter nuclei of the second 
mitosis; and where the tetrads are formed by one longitudinal 
and one transverse division of the segment of the spirem, it is 
equivalent to reduction in the prophase of the first division, 
? BELIAIEFF, W.: Ueber die Reductionstheilung des Pflanzenkernes (Vorlaufige 
Mittheilung). Ber. d. deutsch. bot. Gesells. 16 27-34. 189 
3Chromatin reduction and tetrad formation in nesta ees Contrib. Dept. 
Bot. Columbia Univ. 5: 101-115. i. 295, 296. an 
