348 CuHuuRCH: THE BULB IN COOPERIA DRUMMONDII 
this pull, which results from the contraction of the roots, and is 
gradually placed more deeply in the ground with each new set of 
roots. Even the upward development of the shoot, where the 
lowest and oldest scales are each formed at a slightly higher level, 
does not counteract entirely this forced downward movement of 
the bulb. Therefore the bulb is continually placed more deeply 
in the soil. 
In Arum maculatum Rimbach (28) explains that the active 
portion of the root consists of the cells directly below the epidermis 
and the ‘‘hypodermal layers.’’ These cells shorten in their length 
as much as one half and their radial walls lengthen somewhat. 
The vascular bundles and their accompanying cells are not active. 
However, the latter respond sufficiently to the vertical pressure 
caused by the shortening of the parenchymatous" cells just out- 
side them to show definite wrinklings along their walls, and the 
tracheal tubes themselves shorten between the rings. 
Rimbach’s careful observations and well-chosen biological 
experiments are not supported by his theoretical conclusions. 
Because he has accurately noted that endodermal cells lengthen 
radially, he proceeds to state that they shorten longitudinally 
_and that therefore the whole root contracts, with the result that the 
bulb is set more deeply into the ground. All other tissues are 
passive, yet they must be shortened in the shortening of the whole 
root. Without sufficient morphological proof Rimbach claims that 
the outer or cork cells are crushed and killed, and that the vascular 
cells are thickened. The outer cells are crushed doubtless, but do 
they die first or are they killed by the crushing? His further con- 
clusion that the vascular cells thicken may be true, but where is 
his proof? To return to the active or endodermal cells, how 
can we accept the statement that because a cell lengthens in one 
direction therefore it must necessarily shorten in another? Vol- 
ume ‘being constant and cell wall composition and tension being 
similar at every point this would be true; but Rimbach did not 
investigate these points. : 
Rimbach states that ripples may be seen on the root surface 
even to the root-ends with the naked eye. Microscopic slides 
have proved to the writer that the process of root contraction is 
well under way in a five-day-old seedling of Cooperia Drummondit 
