CHAPTER XV 

 GRASSES, CLOVER, AND ALFALFA 



The importance of hay crops in the world's agriculture makes 

 desirable their consideration from the standpoint of improve- 

 ment by breeding. Grasses, clover, and alfalfa differ strikingly 

 in (see Chapter III) amount of seed set when artificially self- 

 pollinated. Red clover (Trifolium pralense) is practically self- 

 sterile; white clover (Trifolium repens) sets -few seeds when 

 protected from insect pollination; timothy (Phleum pratense) 

 under a bag produces few seeds; and brome grass (Bromus 

 arvensis) under the same conditions sets seed abundantly. 

 Although common alfalfa (Medicago saliva) and yellow alfalfa 

 (M. falcala) cross freely, seed of either may be produced by 

 selfing. Enough examples have been cited to show that there 

 are not only differences in the modes of pollination in the 

 three mentioned classes of hay crops but also differences within 

 each class. Carefully controlled experiments with grasses to 

 determine the percentage of naturally crossed and naturally self- 

 fertilized seed are very limited. To what extent decrease in 

 vigor will result from artificial self-pollination is also an un- 

 answered question. When self-sterility is not a limiting factor, 

 the methods of breeding all these crops are essentially alike. 

 The ease with which some of them may be clonally reproduced 

 has led to slight modifications in breeding technic. In the 

 following brief discussion, the aim has been to choose a few 

 examples rather than to enter into an exhaustive treatment of 

 the entire field. 



GRASSES 



Timothy ranks far ahead of the other grasses in importance. 

 Some of the other hay grasses which may be mentioned are 

 orchard grass (Dactylis glomerala), tall oat-grass (Arrhenatherum 

 elalius), and brome grass (Bromus inermis). These three grasses 

 are adapted to certain conditions better than is timothy. Some 

 important pasture grasses are Kentucky bluegrass (Poa pralen- 



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