340 Knox: STEM OF IBERVILLEA SONORAE 
phery of the tuber, and like the ground-parenchyma the walls of 
all these cells are pitted and very thick. The periderm renews 
itself constantly and continues to be sloughed off, while the abun- 
dant calcium carbonate gives. 
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Pe ee ee 
the gray color to the entire 
surface. There is no true bark, 
nor are there any deeper-seated 
phellogens. The course of the 
bundles has not been investi- 
gated. De Bary says that the 
bundles of the Cucurbitaceae 
are bundles of the leaf-trace 
running up two_ internodes. 
Accounts are given by Bertrand 
(9) and by Lotar (12), and 
later by Leisering (29) and by 
Tondera (31). The latter, by 
sections and maceration com- 
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bined, has secured details of the 
complicated connection at the 
nodes which he presents in a 
series of elaborate diagrams. 
A reference to the descrip- 
tion of /bervillea (21) will re- 
mind one that this tuber is or- 
dinarily referred to as a root, 
and that its closest analogies 
seem to be the roots of Bry- 
onia and Thladiantha, The 
picture of the old plant (FIGURE 
A), with its shoots rising from 
the tuber, shows the gradual en- 
Ss 
icee largement of the stem, though 
B. /bervillea Sonorae, four or poe 
five years old. the appearance of the seedling 
(FIGURE B) would indicate that 
the swollen portion includes root, hypocotyl and stem. As far as 
this investigation goes the formation is stem, and at least half of the 
swollen portion may claim that distinction, and as the bases of the 
