300 
REMARKS ON SOME VEGETABLE PHENOMENA. 
sequently damp woods, in tropical countries; and from their great 
luxuriance in such situations, it is quite manifest that their numerous 
roots dangling in the air collect from, that medium all the nutriment 
which is necessary for their support. 
There is another description of vegetables which are disseminated on, 
and germinate in the earth, and from thence draw support by means 
of their first roots; but as they advance in age and bulk, other roots 
proceeding from the joints of the stem descend and fix themselves in 
the soil, superseding the original roots, which soon after decay. Such 
plants are the pandanus, or screw-pine; of these an aged plant may be 
seen, supported by a few buttress-like roots, which in their turn also 
(together with the base of the stem itself) perish as soon as new ones 
from above have reached and got hold of the ground. In fact, every 
new set of leaves appears to require a new set of roots for their special 
service ; and which, during their descent, absorb from the air a part of 
the aliment necessary for the sustentation of the large and heavy head. 
There is yet another and extensive tribe of plants called succulents, 
which are remarkable for their heavy and substantial leaves and stems, 
and furnished with a very diminutive system of roots, and moreover 
flourish in the driest and poorest soils—nay even where there is no soil 
of any kind, but merely a chink in a rock, into which a few radicles 
only are insinuated. 
All these circumstances combined go far to prove that, in the 
instances adduced, a great, if not the greatest portion of the elemental 
food of plants is derived from the air, and that this is as capable 
of distending the vascular and cellular membranes of plants as that 
which is received from the earth. If this idea be at all feasible, may 
it not be employed in accounting for some circumstances in the growth 
and development of the cellular and vascular membranes of trees which 
appear to be involved in no little obscurity ? 
By the closest inspection of the gradual accretion or growth of plants 
—whether we take the most minute of the Cellulares , or the grossest 
of the Vascular es —whether we examine with the keenest eye or the 
most powerful microscope, we can only detect a change from small 
to greater magnitude, from a state of indistinctness in which the parts 
can neither be seen or numbered, up to perfect form when both forms 
and numbers are plainly recognisable. An atom of this cellular mem¬ 
brane composed, let us suppose, of twelve distinct cells, may be no 
larger than the head of the smallest pin, in the month of May, will 
be, before the end of August, twelve times larger, not by any additional 
number of cells, because that is impossible, but simply by the enlargement, 
of each of the original twelve. This notion infers that every cell, vessel, 
