You see that the vesicles are not purely ovoid, but that they have a convex and a more flattened side. That flat side, we could call the belly side of the bladder animal. The tip of that ventral side is where the blade-shaped projections are. Now the loupe has to come in handy.
At some distance from the tip you see an unevenness in the ventral side, the vesicle skin is bent in there. Now if you take a thin stick or a needle without a point, you can convince yourself that the part from the point up to the bend lies loosely on the edge of the bend and projects a little over it inwards. At the least [ 155 ]touching creates an opening. Now, if a small animal swims against this part, it immediately retreats, and the unsuspecting swimmer, perhaps prompted by his instinct to sniff this dark corner, enters it. Now the lid lies flat on the edge again, only by pulling it could it be raised, but our prisoner has no choice but to push, and that costs him his life.
The corpse decomposes and the putrefaction products, sucked up through the inner wall of the vesicle, are food for the plant. You know that adult daphnias have a shell. That shell doesn't digest, but it can't get the trapped animal out of the bladder any more than before, so it stays there. As the vesicle makes more victims, more of those indigestible remains come, so that it eventually fills up and has to be put out of use. A researcher once found the remains of 24 different animals in such a full vesicle.
Thus a single bladderwort plant, which has a few hundred traps at its disposal, can do a formidable cleanup among the small aquatic dwellers. It is mainly species of Daphnia, Cyclops—all those one-eyed ones—that are caught, but also larvae and even small fish, because the vesicles do grow to ½ cm. big.
In the picture above you can see how even young fish can be caught. The one in fig. 2 accidentally got its tail into the opening, but it can no longer get out, because the valve closes clampingly. How those two vesicles in fig. 3 together have become so powerful that one fish is a mystery, but it happened nonetheless; all the images are drawn from nature by a Russian researcher.
In fig. 4 a cross section of a vesicle is given, twenty times[ 156 ]enlarged, while in fig. 5 very enlarged (400 ×) shows the inner wall of such a vesicle. The protrusions, placed four by four, suck up the nourishing liquid, which is produced by the decomposition of the captive animals.
If you keep Utricularias in a bowl of clean water, they will wither, no matter how well you provide plenty of light. They cannot thrive in clear ditches, where there are no small aquatic creatures. They are literally starving, they cannot absorb enough nutrients from the water: they have to be fed! They are so accustomed to fatty broth that the thin water porridge with which other plants are content makes them sick.
You now also understand that the Bladderwort does not need roots, like the duckweed, for example. The leaves more or less serve the purpose of it: nevertheless they absorb the dissolved nutrients. The hornwort seldom has roots either, it is so completely surrounded by the nourishing water that it is completely permeated by it of its own accord. That "by itself" is of course in a manner of speaking—I mean about the same as when I say that water, in which a pig 's bladder is suspended full of milk, turns itself into water and milk—the milk in the bladder too—you understand again: Physics, Chapter so much, on Osmosis.
The duckweed needs its roots; the underside of the plant alone would not be able to absorb enough. Waterweed could do without roots as far as food is concerned, but he needs them for something else. Most aquatic plants have roots that either hang freely in the water, as in duckweed, or cling to the ground as in waterweed, yarrow, water lilies, water gentians, pondweeds, etc.[ 157 ]
Vesicles of the bladderwort with prey. At 5 the inner wall with suction cells is very much enlarged.
Vesicles of the bladderwort with prey. At 5 the inner wall with suction cells is very much enlarged.
[ 159 ]
The roots come in handy when the ditch empties or dries out. I have already told you that duckweed will not then share the fate of the fish, but will resign itself to continue to live on the mud.
Yes, the fish die when the ditch dries up, save the eels; they creep at night through the grass, wet with dew, to another water palace. Larvae pupate on such an occasion, if they are not too young; I need not tell you that the frogs and salamanders and beetles manage to save themselves. Very small aquatic creatures wrap themselves in a double skin during drought, so they sleep over the drying time and are revived by a puddle of rain.
Now most aquatic plants, which take root in the soil, can withstand adversity well. Utricularia and hornwort die inexorably, but yarrow and waterweed and the pondweeds are tough. If the period of drought lasts a little long, their branches wither and die, but the plants themselves are not yet dead.
When the ditch fills up again, new branches sprout from the bottom. These plants are so careful not to expose themselves entirely—their actual bodies are hidden in the damp mud, and are left there waiting for better times. If you dig a ditch bottom, you will easily find those stems or rhizomes. They sometimes retain their vitality for a very long time; years after the drying out for some reason, when the ditch fills up again, immediately leafy stems and flowers develop again. If the drought lasts for a long time, they must finally die, or change their way of life and become terrestrial plants.
However, the latter is only possible for a few; welfare[ 160 ]there are plenty of plants for which it seems rather indifferent whether they are in the water or not—reeds, blistering buttercups, watercress, fieldcress—but these are in fact all real land plants that can withstand a little moisture. Whether they are in the water or not does not change their appearance.
water clover. After a watercolor by Ben Reith in Maarssen.
water clover. After a watercolor by Ben Reith in Maarssen.
But now go and search with me again in July or August from aquatic plants—perhaps we will also find the much-wanted duckweed flowers—then I'll show you another curious little plant. We don't have to search many wide ditches—especially if the water isn't too brackish and dirty, or we've found it. A number of pointed-oval leaves (8 to 9 cm. by 3) float flat on the water, similar to those of the floating pondweed (the tea leaves), but narrower and more pointed, yellow-green in colour. A dM rises in the midst of those leaves. high, some richly flowered, rose-red spikes, the sweetest little flowers—something to look at as well.
Let's try to grow such a plant. It grows far from the shore, so the hook has to be involved and it is not very easy either, the cherry-red flower spike keeps slipping out from under the fork: the plant is firmly rooted in the soil. Now you can grab the tip, hold and pull gently—with little tugs, or the stem will break off. Handsome—it's already broken—broken at the root. What do we have now?
One and a half meters of limp stem, from which long limp stems sprout from distance to distance, bearing the leaves already mentioned at their ends. Actually don't carry, the stems are so limp that they can't even carry themselves; they bind the leaves to the stem, shall we say. The end of the stem, the red flower spike, is firmer: you can keep it upright—but otherwise[ 161 ]the whole plant is a tightrope of history—slack and smooth; everything lies in a lame heap on the grass.
Why should an aquatic plant be sturdy? Yes, a tree must be strong or it will blow over, and the slender stalks of wheat must be strong enough to hold up the ears—but an aquatic plant? It finds sufficient support in the water, as long as its buoyancy is not lost; and this has been taken care of, because stems and stems and leaves are provided with air spaces, swim bladders as it were. Thus an aquatic plant stands upright in the same way as a stick, at the end of which you have tied a stone with a string, remains upright in the water. Duckweed floats on the white hollow tissue that can be seen on the opposite side of the leaves; the triangular duckweed misses that and therefore does not float, but floats like the hornwort, all according to the same law of Archimedes.
Now you also understand why the bloomer of our moor root (Polygonum Amphibium)—that's the name of the plant we caught—must be so firm, it has no support from the water waiting. Let's take another look at the plant. You notice that the lower petioles are longer than the upper ones—correctly, you say, that is, because all the leaves must float on the water, and therefore must be level.
All right, but now imagine this. Now when the petioles are all just that long, and their ends, where the leaf blade is attached, reaches the surface of the water, then the twelve to twenty leaves of our plant come close together, three or four clumped together. to lie on the top of the stem—not an advantageous arrangement really, when you consider that each leaf must absorb nourishing air with its surface. There must be a flaw in our reasoning.
Just look in the ditch; that raises even more[ 162 ]our rose- red spikes, and there the leaves are not so close together, there are even quite large spaces of water between them. How is this taken care of. Dead simple. The stems, the beginning of which is 20 cm. under water are not 20 but 30 cm. long. They lack the strength, for their leaf blade which is 10 cm. above the water, the leaf blade must lie on the water, the stem, which cannot hang up in a bend due to its buoyancy, comes obliquely stretched into the water and the leaf blade is 15 or 20 cm. away from the flower spike—thus the lower leaves are furthest from the stem, and each leaf has plenty of space and air.
Leaves of the bogroot (Polygonum amphibium) left water form, right land form.
Leaves of the bogroot (Polygonum amphibium) left water form, right land form.
Put our catch in the planter box now—botanising jar they say in the shops—we'll have to look at it again later, I hope. Now leave those duckweed plants alone, you won't find the flowers and I have something else in store.
This ditch used to be higher, but for a few years the polder level was lowered; a little pond at the end of the ditch has run dry and has now become a low, bad meadow—still wet and full of rubbish.
Also a multitude of red flower spikes. Compare them with what we in[ 163 ]have the bus and you will see that the flowers match exactly!
But the plants themselves differ as the crow flies—here in the land plant there is no trace of that smooth, limp and elongated. The stem is moderately long, thick and sturdy, the petioles short and strong, the leaves themselves shaggy and brown and sticky. The whole plant is sticky. And yet we are dealing here with the same plant. When we germinate its seeds on the bottom of the water, the water form develops, while when germinated on dry land the landform appears. If a ditch in which the water form grows runs dry, the stem and leaves sink impotently to the bottom and die there, but the rhizome continues to live in the bottom and develops this year—if the season is too far advanced, in the following year—a stout shaggy stem with short-stalked sticky hairy leaves.
A plant of this kind has even been found in our country, which had developed two stems from its rhizome; one in the water, the other on land. Leaves and stems of the two halves did not resemble each other at all, but had taken on the shape that suited them best in their circumstances.
What does that stickiness mean? The flower must teach us that. Just now, when we compared the flowers, you had occasion to see that they are only small, but very gracefully formed. If you look at one of the more than a hundred flowers of the flower spike separately, you will notice that a calyx is missing and that the corolla is a fine pink-red five-pointed bell, within which 5 stamens and 2 styles. At the bottom, between the stamens, you see five yellow spots on the crown. Maybe they shine a little. That's because honey is isolated there, quite a lot[ 164 ]also. That honey —the flower is very proud of it and at the same time very economical with it. The whole world must know, that is, the whole insect world—another do not know the flowers among us—and the announcement is made in two ways.
Firstly because of the colour: the accumulation of hundreds of flowers on a spike makes them stand out from afar, and then because of a fine penetrating scent, which not only fills the olfactory nerves of us humans, but also those of pleasantly caresses the six -legged honey candy. You know that the latter have the olfactory nerves in their antennae—two mobile noses!
You can be sure that a fly, or a bee, or a little bumblebee, will sense that smell, then it will look around and immediately aim for the beautiful red rod. There we immediately see the 5 yellow spots in a crown, they have known for a long time what that means, they hastily grab the flower, stick head and tongue in and feast. Startled as they are, they have robbed the flower of its goodies in seconds; in this way they finish the whole rod and then float on.
Now, however, our peat roots or water many nodes have a special arrangement. Look for a few different flower sprigs together and then investigate the length of the stamens and styles, and you will immediately notice that the styles and stamens in no flower are of equal length. But also—that in some inflorescences the stigmas are so long that they protrude beyond the corolla, while the short stamens do not reach the margin. In other flowering spikes it is the other way around: there the styles are hidden in the crown and the stamens protrude far out. Now what is this good for?
Of course for the cross-pollination. Check it out. When an insect, a small bumblebee for example on a flower[ 165 ]with long stamens, comes to look for his mouthful of honey, then he must touch the five anthers with his shaggy underside. The sticky pollen gets stuck in his hair. With his head he does touch the stamps of the styles. Now he continues. If he now comes to a 'short-styled' flower again, he gets even more pollen on his belly. However, when he visits a "long-styled" flower, its stigmas just touch the spot on the underside of its body, where all the pollen from the short-style flowers is. These stigmas are sticky—the pollen partially adheres to them when the bumblebee leaves, and the eggs in the ovary can develop into germinating seeds.
%20(358).jpeg)