viii 
Journal of Agricultural Research 
Vol. XIV 
Plate 30. Types of primary tissues of the potato: A.—Transverse section of Pw 
part of large stem bundle showing sieve tubes and companion cells in outer 
phloem, type of cambium and medullary ray initials, metaxylem. B.— 
Transverse section through part of the same bundle showing inner phloem, 
pith, and cells of the perimedullary zone.. 252 
Plate 31. Types of primary tissues and elements of the potato: A.—Trans¬ 
verse section through interfascicular region of central cylinder showing 
cambium, outer phloem groups, and endodermis. B.—Transverse section 
through the same region showing internal phloem groups.... 252 
Plate 32. Types of elements of the potato: A.—Radial section of outer 
cortex, collenchyma, subepidermal layer, and epimeris with stomata. 
B.—Tangential section of part of vascular cylinder of partly mature stolon 
showing numerous sieve tubes and two porous vessels. C.—Tangential 
section of young stem showing sieve tubes of internal phloem and pro- 
toxylem. D.—Tangential section of partly mature stem showing cambium 
and medullary ray initials. 252 
Plate 33. Distribution of tissues and type of elements of the potato: A.— 
Transverse section of large stem bundle at time of secondary growth 
showing distribution and type of medullary rays. B.—Transverse view of 
sieve plate of secondary sieve tube. C.—Transverse section through a 
large stem bundle showing type of cells of perimedullary zone and the 
extent of the latter. D.—Transverse view of sieve plate greatly enlarged. 
E.—Radial section through porous vessel, showing type of end wall and 
extent of pitting.. 252 
Plate 34. Distribution of tissues of the potato: A.—Tangential sec don through 
external phloem, showing branching and anastomosing of phloem groups. 
B.—Tangential section through internal phloem, showing branching and 
anastomosing of phloem groups..... 252 
Plate 35. Types and anastomosis of sieve tube of the potato: A.—Enlarged 
view of part of Plate 34, B, showing type of sieve tube. B.—Enlarged 
view through another region of the same figure, showing type and anasto¬ 
mosing of sieve tubes. 252 
Plate 36. Distribution of tissues of the potato: A.—Transverse section of 
lateral bundle of mature petiole, showing distribution of external and 
internal phloem and amount and arrangement of xylem. B, D, E.—Cross 
sections through leaf blade at different stages of development, showing 
differentiation of palisade layer and spongy parenchyma. C.—Transverse 
section of tepiole, showing arrangement of vascular tissue, amount of 
cortex, and distribution of collenchyma. 252 
Plate 37. Root of the potato in development: A.—Radial section through 
modal region of underground part of stem, showing origin of roots from the 
pericycle. B.—Transverse section of partly mature root. C.—Transverse 
section of a young diarch rootlet, showing arrangement of protoxylem and 
protophloem. 35 .—Transverse section of fully mature root. 252 
Plate 38. Development of the tuber of the potato: A.—Section of mature 
stolon, showing general distribution and relative proportions of tissues. 
B. —Transverse section of part of vascular tissue of young tuber and cortex. 
C. —Transverse section of part of vascular tissue of a somewhat older tuber, 
showing the beginning of extensive cell division in perimedullary zone 
and parenchyma of outer phloem. D.—Transverse section of vascular 
tissue of partly grown tuber, showing the distribution of the phloem groups 
after a period of extensive growth in the perimedullary zone. 252 
Plate 39. Development of the tuber of the potato: A-F.—Transverse sec¬ 
tions through parts of tubers at successive stages of development, showing 
origin and development of the periderm... 252 
