I read something posted saying that the most nicotine in tobacco was in the stem. I didn't believe that as back in the 70's and when out of the leafy weed, we would practice the "snorting of the stems" to try and get the famed buzz. For the most part there was only a glimpse of the effect. So I surmised that tobacco's stems would not carry much nicotine either. I looked up on Wikipedia and found this confirmation:
Every part of the plant except the seed contains nicotine, but the concentration is related to different factors such as species, type of land, culture and weather conditions. The concentration of nicotine increases with the age of the plant. Tobacco leaves contain 2 to 8% nicotine combined as malate or citrate. The distribution of the nicotine in the mature plant is widely variable: 64% of the total nicotine exists in the leaves, 18% in the stem, 13% in the root, and 5% in the flowers.