These additives are considered to be toxins that are meant to kill insects, plants, and fungi. That is probably why the growth of the seeds were inhibited. Cigarettes, cigars, and pipe tobacco are prepared using different methods. Perhaps, these different ways of processing can explain why the batch with cigarette tobacco had a higher average of seed growth compared to that of the cigar batch and the pipe tobacco batch. There are many possibilities or explanations as to why the seeds in the tobacco solutions barely grew.
Further investigations can help is narrowing down an explanation of the results.
First, it would be logical to repeat this same experiment a couple more times, just to secure accurate results. Next, if it is possible to obtain many of the chemical substances in tobacco in an isolated form, we could test them on the seeds. For example, if pure nicotine was available, we could experiment with its effects on seed growth. If we could secure raw tobacco that hasn t been treated in manufacturing, we could probably decipher if or if not the additives, such as pesticides and herbicides, in tobacco are the cause of the stumped growth. In addition, since many of the toxins can only be absorbed by humans from gaseous state, maybe the same applies for plants.