198 



THE CELL 



tion is shown in the formation of the so-called cell plate. In order 

 to study this phenomenon, it is better to watch the process of 

 division as it occurs in pollen mother-cells, and in various other 

 objects, rather than to study the embryo-sac of Fritillaria, which 

 uj) till now has formed the basis of our description ; for in the latter 

 nuclear division is not immediately followed by cell division. 



The following description refers to pollen mother-cells of 

 Fritillaria persica (Fig. 94). After the daughter-segments have 



Fig 94. Three stages in the division of the pollen mother-cells of Fritillaria persica 

 (after Strasburger, Fig. 114, Eng. Edition) :/ separation of the daughter segments ; <j for- 

 mation of daughter coils and of the cell-plate; h position of the nuclear segments in the 

 daughter nuclei and in the developed partition wall. ( x 800.) 



separated into two groups, delicate connecting fibrils are seen to 

 be stretched between them ; these, according to Strasburger 

 (VI. 73), are derived from the central portions of the spindle fibrils 

 (Fig. 94 /). After a time, in the middle of the connecting fibrils, 

 small swellings, which look like glistening granules, are formed 

 (Fig. 94 g). They are most regularly arranged, so that they are 

 seen in optical section to lie close to one another in a row. Thus 

 collectively they form a disc, composed of granules, and situated in 

 the division plane between the two daughter-nuclei ; this disc has 

 been called the cell plate by Strasburger. Flemming (VI. 13 11 ) 

 considers, that these are represented in a rudimentary form in 

 animal cells in the above-mentioned (p. 189) central granules, 

 which are found in a few objects. The cell plate is of the greatest 

 importance in plants, in connection with the formation of the 

 cellulose partition wall, which is the final stage in the whole 

 process of division (Fig. 94 h). " The cell plate," as described by 

 Strasburger, " ultimately extends over the whole diameter of the 

 cell, its elements fusing together to form a partition wall, which 

 divides the mother-cell into two daughter-cells." A thin layer of 

 cellulose may soon be distinguished. Meanwhile the connecting 



