320 Colchicine 



which was larger among tetraploids. When large populations were 

 studied, the diploid and tetraploid spikes could be separated by using 

 the size of seeds for comparison. This was quite as safe as making 

 pollen measurements, so the need for counting chromosomes in the 

 preliminary stages of sorting was not required.^- Such rules can be 

 adopted for other projects. 



In regard to vegetative and floral characters, the tetraploids were 

 taller and of stiffer straws; the degree of tillering was lower; and the 

 number of flowers was reduced. But kernel size and weight ex- 

 ceeded ihat of the diploid. However, the hectoliter weight values 

 were lower. Tetraploid steel rye had good sprouting ability and was 

 able to stand the winter conditions as well as diploid rye. There 

 were no marked differences in maturity values between the two types. 

 The baking quality of the flour of the tetraploids was superior to the 

 diploid in the preparation of both the soft and the hard breads.^ 



Morjihologically, the tetraploid rye, like most autoploids, showed 

 the following differences from the diploid: (1) stems were thicker 

 and stouter; (2) tetraploids were taller; (3) leaves were larger; (4) 

 leaves were thicker; (5) leaves were somewhat shorter and broader; 

 (6) leaves were greener; (7) floral parts were larger; and (8) seeds 

 were larger.^^- 



From a practical standpoint, the advantages gained by tetraploid 

 steel rye over the diploid arose from a favorable balance of two positive 

 properties as against the four more or less negative characteristics. 

 The lower seed setting (20-25 per cent) , reduced tillering, lower 

 number of flowers per spike, and tendency to shed basal spikelets, 

 were counterbalanced by the superior baking quality of the Hour and 

 the improved sprouting ability of the seed.^^- 



Artificially produced tetraploids in rice have been made with a 

 number of important varieties.!"-^ The tetraploids were distinctly 

 larger-grained, heavier-awned, and more robust generally. While the 

 grains were heavier, a reduced fertility counterbalances the gain in 

 weight per grain. Here again tetraploids manifest the usual disad- 

 vantage. These raw tetraploids were without immediate practical use 

 for the reasons already well known. Moreover, there was nnuli doubt 

 that by further selection the fertility could be raised high enough to 

 overcome the yield disadvantage from a reduced fertility. 



Another approach to polyploidy as a means for improving rice 

 was made. The F^ hybrids Oryza sativa var. indica X O. saiiva var. 

 japonica are very sterile in some combinations. This sterility has 

 blocked the j^ossible utilization of a hybrid between the subspecies. 

 There is no apparent meiotic irregularity in the hybrid, and the 

 causes of sterility remain unknown. Autotetraploids seldom exceeded 



