171 



The process of crossing in the case of potatoes is extremely simple as 

 the flowers are large and the organs easy of access. The principal difficulty 

 is to find sorts which are properly equipped to participate in this process, 

 since the production of pollen in the case of this plant is very irregular and 

 often meagre. 



Photo by L. H. N. 

 FIG. LVI. Mr. Lundberg crossing potatoes. 



The seeds of the potato are small and numerous being imbedded in the 

 pulp of the "potato-balls" or "potato-apples." The latter are about the 

 size of large marbles and are suspended from the upper portions of the stalk 

 on short stems or pedicles. When the balls are ripe they are gathered and 

 allowed to dry. The seeds are then squeezed out and in early April are 

 planted in boxes in the hot house. The young plants are usually trans- 

 planted once or twice before being planted in the open. By this time all 

 danger of frost is over and both the ground and the air are warm. The 

 tubers produced from these seedlings the first year are usually quite small, 

 about three years being required to attain full size. At the close of the first 

 season's growth the product of each seedling plant is harvested separately 

 (See Fig. 57) and its tubers carefully preserved for the following year's 

 planting. When this time arrives each lot is planted by itself in short rows 

 and elimination goes on from this time forward. The time required in dis- 

 covering the best combination resulting from a cross naturally varies greatly 

 owing to the many factors which must be taken into consideration and to the 

 unusually large experimental error which has to be reckoned with. The 

 field trials must be very carefully conducted and each lot or "line" must be 

 allowed duplicate or triplicate plots. Tests must also be conducted in the 

 laboratory where the final judgment as to quality, shape and general type 

 is made. After about the third year from the seed, when the tubers have 

 attained normal size and type, the methods of conducting field trials with 

 seedlings are comparable in all essential particulars with those followed in 

 testing ordinary tuber selections made from old races. Empirical methods 

 in determining which combination or "variation" as the case may be, is best, 

 must prevail in each case and these must be practised for a sufficient number 



