It looks like its been draining/drinking on smiting for some time and if you look closely you'd see the color of dye in it xylene and phloem
they are the color of dye in this case red
as you can see in this case the celery was left for 30 min. at first you could see that it was going up a bit, then after 24 hrs it went to the leaves and as we broke it in half it was shown that that the f
phloem and xylem had some stains of red dye
they are red
well as water passes through the phloem and xylem the plant drinks it up and water doesn't have color so, as this dyed water passes it shows where it goes from the stem to the leaf