■564 BOTANY OF CROP PLANTS 



ning of their development, the leaves are often simple, but 

 they increase in complexity with age. The single terminal 

 leaflet, which frequently appears alone, is soon followed by 

 two lateral leaflets, and these by others, so that the leaf soon 

 becomes distinctly pinnatifid. 



Considerable differences have been foimd to exist in the 

 appearance of the leaves of the different agricultural varieties. 



Flower (Fig. 232). — The corolla is tubular, with five lobes. 



Fig. 232. — Potato (Solanum tuberosum). A, berry; B, flower in median 

 lengthwise section; C, floral diagram. 



It is white, yellow, purple, or blue in color and i to i)-^ inches 

 in diameter. There is a single whorl of five stamens which al- 

 ternate with the corolla lobes, and are attached to the tube. 

 The stamens are straight, and bear erect, yellow anthers which 

 are longer than the filaments and open only at the top. 



Two kinds of pollen grains have been observed. Those of 

 most varieties are variable in size, irregular in shape, rough- 

 ened, and largely impotent. Those of the other type are 

 smooth, spherical, and potent. The latter kind are found 

 only on varieties which bear fruit. Some varieties produce 

 both kinds of pollen grains, but such plants do not always 



