396 ANNUAL REPORT OP THE Off. Doc. 



tinctive wheat plant. By some this last type of variation is desig- 

 nated as sports or mutations. The fact that variations occur makes 

 improvement possible, however, the manner and extent to which they 

 occur is of fundamental interest to the plant breeder, and to a large 

 degree is dependent on the method of reproduction. 



All plants are reproduced by one of two methods. In one, the sex- 

 ual method, the plant goes through the seed stage previous to which 

 the flower or blossom performs an important function. It is this type 

 of reproduction which is most common in the general farm and garden 

 crops with the exception of potatoes. In the asexual metJiod of re- 

 production, the characters are transmitted from one individual and 

 generation to another by parts separated from the parent plant as 

 in the case of grafting fruit trees or in potatoes when tubers are 

 used. 



The plants which are reproduced by the sexual method are further 

 subdivided into those which are self-fertilized and cross fertilized. 

 In the first class the same blossom contains the essential male and 

 female organs, and are so constructed that fertilization with foreign 

 pollen is almost or entirely impossible as is the case of the wheat 

 plant. In the second class the plant bears two kinds of blossoms, 

 male and female as in the case of the squash or the respective blos- 

 soms as regards sex are born on separate plants, as may be observed 

 with respect to asparagus. Again the plant blossoms may contain 

 both the male and the female organs but the construction is such 

 that fertilization with other blossoms is essential to seed development 

 as is the case with cabbage. Wherever foreign pollen is essential to 

 the development of seed the plant is said to be cross fertilized, of 

 which the examples cited are typical. It will readily be appreciated 

 that variation will be much greater in individuals which are re- 

 produced sexually than those which are reproduced asexually. This 

 may be illustrated by the Baldwin apple which was found as a 

 chance seedling in Eastern Massachusetts in 1742, and which has 

 since been propagated by budding and grafting until the number of 

 Baldwin trees doubtless runs into the millions, yet the general Bald- 

 win characters are present whether the tree be grown near its an- 

 cestral home or hundred of miles away. It is true that there will be 

 some slight variation due to local environmental conditions, but in 

 general the Baldwin characteristics predominate. Likewise in the 

 case of plants which are self-fertilized as wheat, the variation is re- 

 latively slight, and once having selected a superior strain or plant 

 which is superior because of heredity, no further attention need be 

 given to maintaining its purity. On the other hand, plants which 

 are cross fertilized as corn or cabbage produce marked variations in 

 succeedina: generations because of the mixture of other plants each 

 of which has a different parentage. 



With the foregoing facts in mind it is evident that when undertak- 

 ing the improvement of any crop one of the first points to receive 

 consideration is that of the nature by which variation arise, and the 

 extent to which they may be utilized to secure the end desired. Ob- 

 viously plants which are reproduced asexually are less variable than 

 are those in which the sexual method is involved. Therefore, once 

 having discovered a promising variation, it may be rapidly niulti- 



