Jan., 1907.] Synapsis and Synizesis. 43 



stage in the life cycle of every sexual oi-ganism containing defi- 

 nite chromosomes. The fusion of the chromatin in synapsis can- 

 not have anv important effect on the hereditary characters of the 

 chromosome. At the most the effect is probably the safne as that 

 which mav be experienced in the fusion of the chromatin during 

 each resting period of the nuclei in the entire history of the "2x" 

 stage. It is the association of the chromosomes in the oospore 

 and the subsequent vegetative history that appears to be of im- 

 portance whether the chromosomes are closely mingled and 

 fused or not. And it must be apparent that hereditary tenden- 

 cies are active both in the resting stage of the nucleus and in the 

 process of karyokinesis. 



The early longitudinal splitting of the spirem in the first re- 

 duction division may be looked upon as a continuation of the 

 usual process of vegetative karyokinesis, the quantitative separa- 

 tion of the daughter parts being interfered with by the interca- 

 lation of the synaptic stage. Since the separation or segregation 

 of the univalent chromosomes follows immediately, a second 

 division spindle is organized through the influence of the double 

 chromosomes and thus normal nuclei are again produced by the 

 distribution of the daughter halves. The mere presence of these 

 chromosome pairs in the daughter nuclei resulting from reduction 

 may be the cause of the rapid formation of the second spindle, 

 and the explanation of the quite general presence of cell tetrads 

 following the reduction division in both plants and animals. 

 Yet it is hardly permissible to say that the first and second divi- 

 sions are not true karyokineses. Nevertheless, the second div- 

 sion is a karyokinesis which had its beginning in the previous 

 stage which was interrupted by the intercalation of the synapsis 

 and reduction processes. The first spindle formed was taken 

 advantage of by the bivalent chromosomes and the segregation 

 following being of paternal and maternal double chromosomes 

 the second spindle became necessary for the separation of the 

 daughter pieces. In the first division the number of chromatin 

 granules is not reduced although only half the original chromatin 

 granules are represented in the daughter nuclei because of the 

 transverse division of the chromosome as shown by me in the 

 reduction division of Lilium philadelphictiui .^ In such cases 

 as in the megasporocytes of Lilium, where the process of 

 spore formation has been abbreviated, the vegetative division 

 following the reduction is of the same nature as the second divi- 

 sion when the usual spore tetrads are produced. This was defi- 

 nitely shown to be the case in my paper on Erythronium alhi. 



*ScHAFFXER. JoHX H. (Contribution to the Life-history of LiHum 

 Philadelphicum). The Division of the Macrospore nucleus. Bot. Gaz. 

 23 : 430-452, 1897. 



