344 THE AMERICAN NATURALIST [Vol.LVI 



Non-reduction.— In belated pollen-motlier-cells the 

 chromosomes in the trivalents assume the f our-lobed con- 

 dition of those in the adjoining cells which are in the 

 metaphase of the second division. The first nuclear divi- 



TABLE II 



Detachment of Chromosomes. Non-reduction 

 Pollen Tetrads of Triploid Plants. (Percentages) 











































19729 (V)l'.'. 

 19729 (1) d.. 



20345 (1) b'.'. 

 20345 (1) c. . 



90.3 

 98"o 



0.8 0.3 



0.2 



























pollen-g 









sion is entirely omitted, there is no reduction (8), and 

 two nuclei with 36 chromosomes each are formed at the 

 second division. The two cells which result are twice 

 the size of the average microspores, and can be seen in 

 the pollen as giant grains. Non-reduction may be greatly 

 increased by transient cold. It averaged 0.4 per cent, 

 in the tetrads. A hundred full pollen-grains were meas- 

 ured at random. from each of 8 flowers on 4 triploid 

 plants. The average was 0.5 per cent, of giant grains. 



Chromosomes of Functioned Egg-cells.— In one triploid 

 Datura, from three (or fewer) capsules pollinated by a 

 normal, there were produced 75 mature plants, 67 of 

 which had their chromosomes counted. 



