PLATE: 42 
Ontogeny of the potato: 
A. —Transverse section through potato sprout showing metaxylem and primary 
medullary rays. X 450. 
B. —Transverse section through part of growing region of potato sprout, showing 
position of the first formed protoxylem and the differentiation of the internal and 
external phloem groups from the procambium. X 405. 
C. —Transverse section through potato sprout, showing beginning of cambium de¬ 
velopment. X 396- 
D. —Transverse section through distal region of potato sprout, showing the first 
differentiation of internal phloem and protoxylem (X). X 342. 
64611 °— 18—4 
