Mar. 15,1924 
Studies oft the Potato Tubev 
817 
the phloem groups are smaller and more elongated than the storage cells 
and contain only small amounts of fine transitory starch. 
To recapitulate: The tissue outside the vascular ring is composed of a 
ndSr area r of^tn nal ° g0US ° riginal cortex of the stolon and a much 
f stora 8 e parenchyma containing numerous groups of phloem 
This tissue is procambial in origin, although very much changed n ks 
later development on account of the r 61 e which it is destined to plav in 
the function of the tuber as an organ for storage. P 7 
anges such as take place in the pericycle also proceed in the Mark- 
rone. Rapid and continuous cell division causes here also a spreading 
^ ?,G " 3 ' ^ agra mm a ti c drawings 0 f radial X9) and mature tuber (normal size) to show 
tinn^ e ?u Ct ^ n +° u 1116 P hloem groups centripetally. The activity con- 
tinues till the tuber is mature. A certain amount of cell division also 
takes place in the region of the primary xylem whereby the protoxylem 
elements become more and more separated from the metaxylem S seen 
i^inomuspicuous ^ 16 ^ ° f ^ng from such gro^h, howev£ 
In the mature tuber the vascular ring approaches the periphery in the 
Sir 0 ™* 6 f 7 ?’ -“ ng out £r the buds and bffiSes o? 
e latter. The central pith is continuous with the eyes, as can easilv 
When^I tX tUl T ° nly * f t W peters in diamete^ is examS 
When the tuber enlarges and the distance between the peripheral eyes 
