Nov., 1912.] The Reduction Division in Fuchsia. 5 



middle. The next division is longitudinal and the resulting nuclei 

 form the tetrads. The nucleoli fragment and pass into the 

 cytoplasm during both the first and second divisions. 



In Agave viriginica (22) Schaffner described bivalent proto- 

 chromosomes which formed a long delicate continuous spirem 

 with a single row of chromatin granules. Synizesis follows 

 during which there is no union of the spirems. A study of living 

 material did not show any noticeable contraction of the nuclear 

 contents and the nucleoli were usually found occupying a central 

 position in the nucleus. While the chromatin granules undergo 

 transverse division, the spirem shortens and thickens and then 

 twists up into twelve loops of different size and shape which are 

 pressed against the nuclear wall. These loops then break apart 

 into four large, three ring shaped and five small irregular chro- 

 mosomes. One or two nucleoli are present which may be thrown 

 out into the cytoplasm. The spindle is bipolar and at the first 

 division the chromosomes divide transversely but the second 

 division is longitudinal. 



Miss Hyde in her paper on Hyacinthus (11) did not find 

 definite protochromosomes nor a splitting of the spirem. She 

 observed a continuous spirem which formed eight definite loops. 

 These loops break apart and fonii eight chromosomes of different 

 characteristic sizes and shapes. 



There has been much controversy as to the real nature of the 

 contraction generally observed in the early stages of the division 

 of reduction cells. In most cases this contraction is accompanied 

 by an enlargement of the nucleus due to the expansion of the 

 nuclear wall. McClung (15) has suggested the term synizesis, 

 to be used to mean the contraction as distinct from synapsis, 

 synapsis being restricted to the fusion of simple chromosomes into 

 multiple ones. Lawson (12) has recently investigated the problem 

 and his interpretation of synizesis is simply that it represents a 

 growth period of the nucleus — a period during which there is a 

 great increase in the amount of nuclear sap, which results in a 

 distention and withdrawal of the nuclear membrane from the 

 chromatin. As to why the nucleus should swell so much immedi- 

 ately before the reduction division he answers as follows. Each 

 cell is charged with sufficient food substance for the production 

 of the tetrad. Moreover there are two divisions which follow 

 one another in quick succession. The pressure of the cell sap acting 

 from within causes the nuclear membrane to distend and the 

 nuclear cavity to expand. The expansion is at first gradual and 

 continuous until the nuclear cavity grows to twice or even three 

 times its original size. 



As the growth proceeds the membrane is gradually withdrawn 

 from the chromatin mass within. The result of this withdrawal 

 of the nuclear membrane is the formation of a large clear area of 



