200 



BOTANY 



The investigations of C. H. Farr and W. K. Farr have shown 

 that furrows which are developed from the periphery inwards are 

 mainly responsible for cytokinesis in angiosperm microsporocytes. 

 It was discovered that in Nicotiana the four pollen nuclei, at the 

 conclusion of the homotypic division, are all connected by achro- 

 matic fibrils. The two sets of connecting fibres from the second 

 division may persist and four new sets are added, or occasionallv, 

 the two sets formed at the second division may disappear and 



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Fig. 74. — Development of achromatic figure in root tip of Ilijacinthus. (1) Stage 

 of greatest prophasic nuclear enlargement. (2) Polar caps present, due 

 to shrinkage of nuclear membrane. (3) Nuclear membrane partially 

 vanished, caps about to develop into spindle cones. (4) Spindle cones 

 established — metaphase. Note chromosomes do not invade spindle area. 

 (After Robyns, from Sharp, Introduction to Cytology.) 



six new sets are formed anew. Although these fibres may show 

 thickenings here and there on their surface, they take no part in 

 the formation of the separating walls. Constriction furrows now 

 make their appearance at the periphery and proceed to grow 

 inward until finally they meet in the centre and the protoplast is 

 thus simultaneously divided into four spores. The formation of 

 walls in Nelumbo lutea has also been investigated by Farr. It was 

 found that at the conclusion of the homotypic division the four 

 daughter nuclei enlarge very considerably, reaching approximately 

 four times their former volume. Quadripartition of the cell now 

 takes place by furrowing. This begins by the appearance of a 



