VARIETIES OF WHEAT 65 



Its own flower, while the rest is deposited into the open air. 

 As the glumes are open upward there would seem to be nothing 

 to prevent the flower below on the same spike from receiving 

 this pollen. Cross-fertilization bet^veen flowers of the same 

 spike would seem probable, while cross-fertilization between 

 flowers of different spikes in close proximity would seem possi- 

 ble. In practice, however, it is found that different varieties of 

 wheat gro\Mi side by side rarely cross, although it has been 

 pretty definitely proved that they sometimes do so. It has not 

 been satisfactorily explained why varieties do not cross under 

 these conditions. Cross-fertilization can readily be accomplished 

 artificially. It has been suggested that it may be due to the 

 stigma being more receptive to the pollen of its owti flower than 

 that of other flowers. Rye, a closely allied species to wheat, 

 seems to cross readily. The pollen is often seen floating over 

 a field of r^'e at the proper season of the year. The anthers 

 are much larger in r}'e than in wheat, and therefore the pollen 

 more abundant. The abundance of pollen, the ease with which 

 it floats in the air and the time of day at which the flowers open 

 may be factors in this problem. (49) 



106. The Law of Cross-Fertilization. — It is a generally recog- 

 nized law that cross-fertilization adds vigor to the offspring, and 

 the many devices by which this is accomplished in plants forms 

 a very interesting study. Hays has suggested that Darwin's 

 dictum that nature causes benefits to arise from crossing and 

 abhors self-fertilization may not apply to all plants. He 

 would state the law thus : *' Nature abhors a radical change 

 which would require species to cross in much closer or in much 

 more radical relationship than is their long-established habit," 



107. Importance of Crossing as a Method of Improvement. — 

 Mendel found that hybrid peas selectea to one tyipQ were soon 

 stable. Mendel's Law worked out formally gives the following 

 results as applied to one characteristic ot the artificial hybrids 

 allowed to self-pollinate during a series of years. 



