448 On the upright Growth of Vegetables. [Juny, 
in the soil. The fern grows in this way also; and it is evident that, 
whilst growing in that position, it is the upper side of all these 
plants which elongate the most. A more common example is 
afforded by trees much exposed to the wind. ‘They invariably 
elongate on the upper or windward side; and it may be thence laid 
down as a general rule that the trees of this country have their 
longest side to the south-west. I shall only adduce one fact more, 
somewhat similar in its nature, and equally decisive against the idea 
of an accumulation and luxuriance of growth being a consequence 
of deflection. ‘The sap always flows most freely on the south side 
of trees exposed to the sun. It is where the sap flows most freely 
that the tree grows with the greatest lusuriance. Of course where 
the under side happens to be the north side, which in this country 
is most generally the case, the under side grows less luxuriantly 
than the upper side. 
Thus ali the phenomena exhibited in the growth of plants oppose 
themselves to Mr. Knight’s hypothesis. The analogy of nature is 
equally arrayed against it. Unity and simplicity are the great cha- 
racteristics of Nature’s laws. ‘The vast importance of the object 
attained by the perpendicular growth of vegetables, and the simple 
means by which that object is attained, form a beautiful illustration 
of this obvious remark. The provision that plants shall grow 
upwards secures for the animal creation the greatest possible quan- 
tity of vegetable food ; and for effectuating this simple arrangement 
we expect to find an equal simplicity in the mechanism employed ; 
to find some principle which directly communicates to plants an 
upright rectilineal direction. Under the influence of such a train 
of thought, we cannot for a moment believe that perpendicularity 
is the effect, not of any immediate agency, not of any directly 
buoyant or centrifugal force, but of a continued series of cor- 
ections. . 
In what manner, then, does the principle of gravitation act ? 
To what part or circumstance is its influence directed? I am well 
aware that it is much easier to overturn an erroneous theory than to 
produce in its place one free from error; yet as the same reasoning 
which led me to the conclusion that gravitation was the operating 
princip'e, leads almost with equal force toa conclusion as to the 
particular mode by which that principle acts; and as the one has 
been already verified by decisive experiments, I am emboldened to 
hazard the other, which from these circumstances may lay claim to 
presumptive evidence in its favour. 
In a former paper, which 1 had the honour to read to this Society, 
it was endeavoured to be explained how gravitation or attraction 
produced a perpendicular ascent ; and it was stated as the universal 
law governing all perpendicular ascents and descents, “ ‘That as in’ 
the case of direct attraction (that is, where the bodies are at liberty 
to move in the line of attraction), the body most attracted leaves 
the body least attracted ; so when attraction is resisted the reverse 
happens, the body least attracted leaves the body most attracted, but 
