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252 DESIGN IN NATURE<br />
vacuoles, spaces, or cavities of about ttoVtt of an inch in diameter, which contract with regular rhythm at intervals<br />
of from thirty-eight to forty-one seconds, quickly contracting and then more slowly dilating again."<br />
Sir James Paget adds : " The observations of Cohn,^ pubhshed about a year later than those of Mr. Busk, but<br />
independent of them, discovered similar phenomena in Gonium pectorale and in Chlamydomonas , the vacuoles, like<br />
water-vesicles, contracting regularly at intervals of forty to forty-five seconds. The contractions and the dilata-<br />
tions occupy equal periods, as do those of our own heart ventricles ; and in Gonium he has fovmd this singular fact,<br />
that when, as commonly happens, two vacuoles exist in one cell, their rhythms are alike and exactly alternate,<br />
each contracting once in about forty seconds, and the contraction of each occurring at exactly mid-distance between<br />
two successive contractions of the other. Here, then, we have examples of perfect and even compound rhythmic<br />
contractions in vegetable organisms, in which we can have no suspicion of muscular, structure, or nervous, or of<br />
stimulus (in any reasonable sense of the term), or, in short, of any of those things which we are prone to regard as<br />
the mainsprings of rhythmic action in the heart." ^<br />
The movements in the insectivorous plants are more or less rhythmic and definitely co-ordinated. They are<br />
also movements to a given end, and purpose-like, namely, the securing of living flies and small insects as food.<br />
Examples of these movements are to be seen in Venus's fly-trap {Dionma muscipula) and the sun-dew (Drosera<br />
rotundifolia). Arrangements for catching live insects are also met with in the pitcher plants.<br />
In Venus's fly-trap the outer portion of the leaf bifurcates, is orate, slightly saucer-shaped, and provided with<br />
serrated edges and six exceedingly sensitive hairs, three on each half of the leaf, which project from the surface,<br />
and are consequently in the way of anything moving on the leaf. When any small insect (fly, beetle, &c.) settles<br />
and crawls on the leaf it inevitably comes in contact with the sensitive hairs, and the plant, being informed of the<br />
presence of the insect, slowly but surely imprisons, crushes, and destroys it. Nor does the marvel stop here. No<br />
sooner is the insect fairly within the grasp of the leaf than a secretion, akin to gastric juice, is poured forth from<br />
glands on its surface which enables the plant hterally to devour and assimilate the insect. The leaf remains closed<br />
until the process of assimilation is completed, when it gradually opens to receive a new victim. Nor is this all.<br />
If the plant be tricked by dropping a small piece of cork or some non-edible particle on a leaf, it closes the leaf, but<br />
soon again re-opens it ; no digestive fluid whatever being exuded. The plant can therefore distinguish between<br />
what is edible and what is non-edible. This impUes a low form of cognition or its equivalent. The opening and<br />
closing of the leaf and the production of a digestive fluid cannot be regarded as, in any sense, haphazard.<br />
When we consider that the spontaneous, definite, co-ordinated movements of Venus's fly-trap are performed<br />
m the absence of bones, muscles, nerves, and all those structures which are usually associated with the production<br />
of purpose-hke movements in animals, they are, to say the least, very remarkable. They, in a sense, widen the<br />
horizon of organic movement indefinitely. They show that the potentiahties of Uving matter are practically un-<br />
hmited. Motion, purpose-hke motion, can no longer be regarded as the prerogative of animals. That the move-<br />
ments of the fly-trap are not due to irritation in the ordinary sense is proved by this, that they will close on living,<br />
edible, and dead, non-edible particles ahke. There is, however, this astonishing difference : the leaves remain closed<br />
on edible particles until they are digested and assimilated, whereas they open and extrude non-edible particles.<br />
If the food of the plant acted as an irritant, the plant would naturally get rid of it with all possible haste. This,<br />
as explained, it never does. The substances which it will not tolerate are the non-edible ones.<br />
RHYTHMS AND REFLEXES IN PLANTS AND ANIMALS: THEIR<br />
NATURE AND USES<br />
Rhythms in plants and animals may be defined as involuntary movements recurring at stated intervals •<br />
movements bemg repetitions of each other, and the intervals varying according to circumstances. They are funda-<br />
mental inherent, and intimately associated with hfe in its several phases : indeed hfe without rhythms would be<br />
impossible, as they are, to a large extent, the means by which nutrient materials are added to hving bodies and the<br />
detritus or waste products carried off. They, in conjunction with certain reflex acts, are responsible for aUmentation,<br />
respiration, circulation, reproduction, secretion, excretion, and various important functions, the due performance<br />
of which IS necessary not only to the well-being but also to the existence of the individual. The rhythm, make their<br />
appearance at the very threshold of life in rudimentary plants and animals as contractile vesicles, and they<br />
Zr TU^"Z"f^r7<br />
"^ "" -'"f '" ?.' ''''''' °' differentiation attained by plants and animals respec-<br />
tively. Ihis IS especially the case m ammals. Rhythms, in the mdest sense, are accountable for most if not all<br />
L,oo„,a,> Lectuio, On the Ca,>so of the El.ythnuc Motion of the<br />
•28, 1857<br />
Heart," l,y Su- James Paget, Bart., F.R.S. Proc. Roy. Soc, May<br />
the