109 



are closely packed, and are so numerous that counting is impossi- 

 ble. In the early stages, however (Figs. 8 and lo), it can be seen 

 that the number is about sixty. 



The compact arrangement of the tetrads in the nuclear plate 

 leaves no chance for orientation. It is impossible, therefore, to 

 tell from this division whether the tetrad divides through the line 

 of original cleavage, or through the secondarily acquired trans- 

 verse cleavage. In other words, it is impossible to tell whether 

 the division of the primary sporocyte is a reducing or an equation 

 division. There is, however, good reason to regard this as an 

 equation division, and the division of the secondary sporocyte as 

 transverse, and, therefore, as a reducing division. The second 

 mitosis follows closely on the first, but in the short interval the 

 two parts of each dyad, which at first appear like two small balls 

 closely pressed together (Figs. 12 and 21), now become drawn out 

 in the direction of their common axis, which is probably the 

 original longitudinal axis of the spireme-segment (Figs. 13 and 

 14). It is immaterial in the final spore cells whether the first or 

 the second division is a reducing division in the Weismann sense. 

 That one of them must be is shown by the method of tetrad 

 formation ; but, from the manner in which the dyads elongate, the 

 probability is certainly strong that reduction is effected by the 

 second mitosis. The change in shape of the chromosomes in the 

 secondary sporocyte-spindle makes the general appearance of the 

 nuclear plate conform more nearly with that of the somatic cells 

 (cf. Figs. 13 and 18), although they are fundamentally different. 



4. TJie spore. 



The cylindrical shape of the daughter chromosomes as they 

 come from the division of the dyads in the secondary sporocytes 

 is retained until late in the anaphase (Fig. 14). The resulting 

 four daughter-nuclei lie freely in a single cell which, until the cell- 

 plates are formed, is a syncytium. In the division of multinuclear 

 cells it has been frequently noted that the nuclei are connected by 

 spindle fibres. This occurs in ferns, and long after division, and 

 even as late as the telophase after the cell-plates are formed and 

 the nuclei have gone into the resting stage, fibres can still be seen 

 connecting each nucleus with all the others (Figs. 14 and 15). 

 While the cell-plates are forming, the chromosomes gradually dis- 



