392 BOTANICAL GAZETTE [MAY 
forming a continuation or outgrowth of a marginal parenchyma 
cell. Such appearances are fairly common in all three species of 
Cedrus. These observations may throw some light on the origin 
of the marginal parenchyma. THompson (8) in his account of 
the marginal parenchyma which occurs sparingly in Abies suggests 
that these cells have arisen in connection with the demand for food 
storage which occurs at the close of the growing season. ‘The close 
association of marginal parenchyma with resin cells in Cedrus sug- 
gests, however, that the two structures may have arisen at the same 
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2 
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Fic. 5.—C. libani, root; one of the erect cells bears crystals; 290. 
time, or even that the vertically elongated marginal parenchyma 
cells gave rise to rows of resin cells. Of the different positions 
occupied by resin cells, the terminal position found in Cedrus appears 
to be the original one; at any rate, the plastic materials for supply- 
ing such cells are more abundant at the close of the growing season 
than at any other time. If we consider a marginal cell just cut 
off from the cambium, it is easy to see that if such cell is in con- 
tact with a resin cell which is being supplied with material from the 
medullary ray, the marginal cell will have a tendency to remain 
alive rather than thicken its wall and die, that is, develop into a 
marginal tracheid. 
