OF AMMONTA ON THE ROOTS OF PLANTS. 261 
with granular matter. It appears, therefore, that matter of some 
kind must have passed laterally from those rows which do not 
contain granular matter, after being acted on by the ammonia, 
into the adjoining rows. Why the useless matter should not pass 
out of the root through the outer walls of the cells, probably 
depends on the thickness and cuticular nature of the outer walls, 
Pfeffer states that root-hairs are developed on the gemme, 
and apparently on the thallus, of Marchantia polymorpha from 
superficial cells which, even before the growth of the hairs, do 
not contain starch- or chlorophyll-grains ; although these bodies 
are present together with matter of an unknown nature in the 
adjacent superficial cells. He has observed a nearly similar case 
with the roots of Hydrocharis*. No one else seems to have 
even suspected that root-hairs were not developed indifferently 
from any or all of the exterior cells. But it has now been shown 
that with many plants, with only one marked exception, namely 
that of Cyclamen, the root-hairs arise exclusively from cells in 
which granular matter has not been deposited after the action of 
certain solutions. This relation between the presence of hairs 
and the contents of the cells cannot be accounted for by matter, 
Which would have been deposited if the roots had been subjected 
to a proper solution, having been consumed in the formation of 
the hairs; and this notion is wholly inapplicable to the cases 
described by Pfeffer. May we believe that cells filled with effete 
matter become unfitted for absorbing or transmitting water with 
the necessary salts, and do not therefore develop root-hairs ? 
Or is the absence of hairs from the cells which contain the de- 
posited matter due merely to the advantage which is commonly 
derived from a physiological division of labour? This and many 
other questions about the cells, in which granules or larger 
masses of translucent matter are deposited after certain solutions 
have been absorbed, cannot at present be answered. But I hope 
that some one better fitted than I am, from possessing much 
more chemical and histological knowledge, may be induced to 
investigate the whole subject. 
* 'Arbeiten des botan. Instituts in Würzburg, Band i. p. 79. 
LINN. JOURN.— BOTANY, VOL. XIX. z 
