An1cca, it is already some time I have read this. I didn't remember you've had taken samples from different parts of the cactus. I am really glad this info is available.

Please correct me if I am wrong...

I suppose we are talking about the picture attached to this post.

1. This is not telling us anything about the correlation between the age and M content.

2. It seems that for the bottom parts of the cactus the concentration is lower than for the upper parts.

3. It seems that this difference is increasing with the size of the cactus.

4. We don't know whether the increase of M content in the upper part is due to the increased production in that part, decomposition or outflow of M in bottom part or transport of M from the bottom to the upper parts of the body of the cactus throughout the lifetime of the plant.

5. We don't know whether previous findings are valid, because the results were done for different specimens and not for the same specimen of different age/size

6. We don't know whether seeming gradient is present both for cactus grown from seed and cactus grown from clone taken from mature plant.