196 The Botanical Gazette, [May, 
definitive size of these cells would be the same as that pos- 
_ sessed several weeks after the application of a cast, for in that 
period the cortex has reached the full extension allowed by 
the circumstances and any subsequent expansion will be con- 
fined to the bundles. In this case, then, we may reckon the 
size of the cortical cells after the cast has been around the 
stem for several weeks as the definitive size; whence it fol- 
lows, that, like the pith, the cortical cells will reach their de- 
finitive state with longitudinal and cross-diameter much less 
than in normal growth. 
De Vries and Krabbe in the writings already cited record 
the fact that the elements of the xylem, when growing under 
strong external pressure, will not attain their normal size. 
My experiments have confirmed this result in every plant 
used. The difference between the size attained and the nor- 
mal size differs in various species. In Eryngium planum it 
was found in one plant to be as two to three; in one plant of 
Pterocarya fraxinifolia as one to two. 
Not only the xylem part of the bundle produces elements 
of smaller size but the phloem also; though a smaller size for 
the cambium cells could not be demonstrated. These Krabbe 
found in his experiments to retain their normal size under all 
pressures; and it will be remembered as already cited in these. 
pages that Pfeffer found the size of the meristematic cells of 
the growing points of roots and stems to be unchanged when 
growing in gypsum casts. ‘al 
Regarding the ultimate thickness of membrane attaine 
by cells growing against pressure, it may be said that the 
mental tissue does 
not seem to be decidedly affected. There are many ¢ 
known where the cortical cells, for instance, 
elongation has ended, thicken up their membran 
ably. Such membranes have in my experiments 
found to become thicker within the casts than norme) 
they seem to remain much thinner. It is to be understo 
here that in this group of experiments th 
when the stems were very young and while fun 
was in its primary thin-walled condition; 
differentiation into mechanical cells is not rer 
only the even thickening of the parenchyma as It 
definitive condition. This thickening seems 
within the cast as well as out of it though the cel 
never 
the subsequent? 
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assumes its 
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