Please find enclosed a document which could throw some light on the question in discussion...

how large are the plants, and for how long do you want to treat them? There are at least 2 ways i have used.

You haven't mentioned what sort of plant, but for grass species:

NEW METHOD FOR SUPPLYING SUBSTANCES TO CEREAL INFLORESCENCES

By:MA, BL (MA, BL); SMITH, DL (SMITH, DL)

CROP SCIENCE Volume: 32 Issue: 1

Pages: 191-194

DOI: 10.2135/cropsci1992.0011183X003200010039x

Published: JAN-FEB 1992

Dear Madam

Plants are having very sophisticated transport system ( Fresh materials) - the phenomena called Ascent of sap.

So in a continuous channel any obstruction is going to happened / it can be made in an artificial manner , the chopped portion of the stem is intact with the solution, we can find the solution entered in to the part of the stem after some time of the duration

pressure injection of trees is a fairly commonly used technique that can be modified and miniturized for small plants. I have used a modified 18 ga needle to inject into small stems.

John P Wright , I am trying to inject into Nicotiana Tabacum xylem/phloem. How would you recommend proceeding?

I used to modify an 18 ga needle by regrinding a taper on 2 sides, then bending the sharp points to make a circle in front of the lumen of the needle. You need to keep plant material from going into the open shank of the needle. I also polished the tip. The needle can be attached to a syringe, or a fine, closed glass tube. In use, the tip of the needle is pressed into the stem. If in the phloem, there will be an increase in pressure, if in the xylem there will be a decrease in pressure. If the sealed tube is prefilled with a solution, the change in pressure can be monitored by change in volume. To inject, slightly warming the tube will force some solution into the stem.

John P Wright , thank you very much for your answer. Unfortunately, I'm struggling to visualize your modification method. Would you be able to share an article illustrating your final needle used?

unfortunately I do not have any pictures. The technique is fairly old, I used it on woody and herbaceous stems. You might search for manometric technique, or look at

Journal of Experimental Botany, Volume 17, Issue 2, May 1966, Pages 283–296, https://doi.org/10.1093/jxb/17.2.283 If you simply push a fine syringe needle into a stem, it becomes occluded by plant material. Reshaping the point prevents this plant material from being pushed into the lumen of the needle.

Thank you very much.

Solutions can be inserted into a plant’s xylem or phloem through a process known as foliar feeding. This involves spraying a solution of water and nutrients directly onto the leaves of the plant. The solution is then absorbed by the plant and travels through the xylem and phloem to the rest of the plant. This process can be used to provide essential nutrients and minerals to the plant quickly and efficiently.