Activity 2 in Chapter 7 of the NCERT textbook for Science (Class 6) is an experiment which the textbook claims to establish that the stem transports water and minerals to different parts of the plant. It involves adding a few drops of red or blue ink to a glass filled one-third with water, and dipping in it a soft stem cut off from its base as shown below-
Below are the photographs of my (imperfect) recreations of this setup-
From left to right:
Plants E, F, G and H
The textbook then requires the reader to make a few observations. I will now quote from the textbook what observations are to be made.
1.“Observe the set-up. Does the colour appear in the stem?”
2. “You will find that the colour rises in the stem.”
3. “If this is kept for a longer period, the colour appears in the veins of leaves also.”
Let us now examine whether these observations hold true for the above plants.
The first two photographs (counting from left to right) were taken when the experiment began. The third was taken a few hours later. In the case of plant A, after a few hours of having been dipped in the ink-water, it began to wilt. Neither the stem nor the leaves acquired any noticeable red colouring. It is possible that although the red colouring is not visible in the stem and leaves, perhaps the inside of the stem would show it. With this intent, I chopped off another portion of the stem.
It is evident from the above photograph that this also is not the case. After some more time, the plant became completely limp (as shown below) and was discarded.
The next set of plants (B, C and D) was plucked in the evening and was allowed to remain in the ink-water overnight. This was done to avoid exposing the plant to the heat of the sun during the day as it may have been responsible for the previous plant (A) wilting.
The next morning, these plants were found to be in this condition-
In the evening of the same day, the plants (B, C, and D) were found to be in this state-
Surprisingly, all the ink had vanished from the bottle in which plant D was kept! Either someone accidently knocked down the bottle, refilled it with just water, and hid this incident from me, or plant D is capable of sucking up ink selectively, and leaving behind only water! Furthermore, there is some water condensation inside the neck of the bottle with plant D. It is unclear why this happened.
The next step would be to cut off a bit of the stem of the plants and observe if it shows any red colouration.
Here, we see that the mystery deepens. Plant D shows no red colouration (in spite of all the ink vanishing) while Plant C shows a very slight red colouration. I also realized that I did not take a photo of the cross section of the stem of plant B though, unfortunately.
For the next trial, aquatic plants (E, F, G, and H) were used. The credit goes to a gardener working at my neighbours’ home. It never occurred to me to use aquatic plants.
The day after they were dipped in ink-water, they were found to be like this-
Unlike the other plants, these were able to survive for a long period of time in the ink-water. Five days after this photograph, the plants were observed to be like this-
As can be seen, the ink has not yet appeared in the stem or leaves. Also, the leaves and stalks of plant H have turned black. This could be a sign that the plant is rotting.
Consider these photographs, taken an entire week after the previous one-
Plant H has turned black. But it also displays substantial red colouration as well. It is not clear what role the rotting of the plant has to play in its colouration. Plant G also seems to have acquired a red tinge in its leaves.
At this juncture, let us revisit the observations we were asked to make and take stock of whether they hold true or not.
“Observe the set-up. Does the colour appear in the stem?”
It was only in the case of plant H this was observed, and that too, after it had rotted. But on viewing the inside of the stem, a slight tinge of red was observed in the case of plant C also.
“You will find that the colour rises in the stem.”
If this were to mean that one can see the ink rising up the stem, from the outside, without cutting off a cross-section, then this was not observed in the case of any of the plants considered.
“If this is kept for a longer period, the colour appears in the veins of leaves also.”
This was observed to be true in the case of plants G and H.
Here, we can revisit the question of whether there is such a thing as an ‘empirical’ claim. This topic had come up in our analysis of the introductory section of the chapter in the textbook. The relevant post can be accessed here. Since there were many plants which did not show any red colour in the leaves and stem, and also a few which did, we can safely say that it is not something which is true by definition. Therefore, it seems that there are claims which can be verified empirically.
Let us now consider the next few statements made in the textbook activity-
“How do you think (emphasis: my own) the colour reached there?”
The previous three instructions required us to make observations using our sight. We observed (in some cases) that the leaves and the inside of the stem acquired a red colour. This question however, requires us to think. This brings us to an important aspect of the scientific practice, which is that there are many situations where we cannot answer questions in science purely by observation. We rely on our intellect and imagination to fill in the gaps between what we observe. The major point of divergence between different theories of the scientific method and different schools of thought within philosophy of science is to do with what they take to be the relationship between observations (acquired through sense experience) and imagination (using the mind). Let us explore this topic in relation to the next statement made in the textbook.
“From this activity, we see that the stem helps in upward movement of water. The water and minerals go to leaves and other plant parts attached to the stem.”
To make this conclusion, we rely on the principle of continuity in motion. We can observe that the plant was dipped in a red liquid and also that different portions of the plant turned red after being dipped in it. Based on this, we imagine that the liquid moved upward through the stem and reached those portions. The notion of continuity in this context is simply that if we consider any two points on the path taken by the liquid, there is always another point in between those two points. In 3 dimensional space, the idea is simply that there always exists a point with Cartesian coordinates whose values lie between the Cartesian coordinates of both those points, through which the liquid has travelled too. What distinguishes imagination in science from that in other disciplines is that in science, we do not stop at merely filling in the gaps of observation with imagination, we also require that such imagination stipulate predictions which can be verified by further observation. In this case, we can confirm the principle of continuity in motion by observing if in between any two points in the plant where the colour was observed, there is another point where also the colour can be observed. It is through these alternating cycles from observation to imagination, and imagination to further observation, and so on, that science acquires its effectiveness.
Nevertheless, we must bear in mind that based on the experiments carried out, we cannot come to the conclusion stated above. For most of the plants considered, we were not able to observe what the textbook predicted. Does this mean that it is not true that the stem transports water and minerals to different parts of the plant in an upward direction? We shall consider this question in the next post.
Moreover, during the course of carrying out these experiments, we made a few observations which lead to some questions-
1.Why did all the plants other than the aquatic plants wilt within 24 hours of their being plucked and dipped in ink-water? To elaborate, the question is that of what series of events lead to a plant wilting.
2.Why did the ink vanish in the setup involving plant D even though it could not be observed in the leaf or stem?
3. Why was there condensation on the inside of the bottle in which plant D was kept?
4. Why did plant H gradually turn black? What is the black colour due to?
5. Why did some plants show red colouration while others did not?
To these questions also, I will attempt to find answers in the next post.
This article is part of a series attempting a philosophical analysis of biology as encountered in NCERT textbooks. To read the concept note for the series, click on the link below-https://barefootphilosophers.org/concept-note-for-series/