ii6 THE STRUCTURE OF ECONOMIC PLANTS 



the axis as the plant matures. (Fig. loi.) The phyllotaxy is 

 both opposite and alternate; and, ordinarily, the lower leaves are 

 arranged in opposite pairs while the upper ones are alternate. 

 Schaffner (15) has reported changes of opposite to alternate phyllo- 

 taxy as a result of rejuvenation 

 by means of variation in the 

 photoperiod. 



The leaves are palmately com- 

 pound, with from 5 to 11 

 leaflets, 7 to 9 being the usual 

 number. These are rough, dark 

 green above, somewhat lighter 

 on the abaxial surface, linear to 

 lanceolate and tapered at both 

 ends, with serrate or dentate 

 margins. They vary in length 

 from 5 to 15 cm., are i to i cm. 

 in width, and the petiole is 4 

 to 6 cm. long with persistent, 

 pointed stipules at its base. In 

 the leaves which subtend the 

 inflorescences, the number of 

 leaflets is reduced to three or 

 even to a single large leaflet 

 with very small awl-shaped 

 laterals. 



The Root. — The root system 

 consists of many radiating lat- 

 erals arising from a primary root 

 that extends vertically down- 

 ward to a variable depth depend- 



(Reproduced from Yearbook of U. S. Dept. of ■ ^ ^j^^ character of the 



Agrtculture, K^iT,.) ", tt ^ ^ i u i 



sou. Heuser Q15J has observed 

 that roots may penetrate to a depth of i meters in well-cultivated 

 soil with a permeable subsoil; but where the plants grow in a 

 heavy humus soil, the main tap root seldom reaches a depth in 

 excess of 30 to 40 cm. The horizontal spread of the lateral roots 

 also depends to a large degree upon the soil type. In mineral 

 soils, where the primary root penetrates deeply, the laterals arise 

 chiefly from the upper 10 to 40 cm. of the axis, and the largest of 



Fig. ioi. Left, carpellate hemp plant; 

 right, slaminate plant held up for comparison. 



