Flowers

http://upload.wikimedia.org/wikipedia/commons/f/f4/Verbascum_thapsus_'Aaron's_Rod'_(Scrophulariaceae)_flower.JPG

Mullein flowers grow on large towers during the plant's second year. The flowers are small (1-2 inches) and yellow. Judging from the picture above: the flowers are perfect having both the female stamen/ovary and the male pollen producing anthers.

The flowers have 5 peddles, 5 anthers on 5 filaments, and one stigma. The anthers are very fuzzy to catch pollen onto any insect that passes. The stigma moves from the side to being in the middle as the flower ages. This is to prevent self-fertilization by having the anthers and stigma mature at different times.

http://www.thehealersbible.com/uploads/1/2/9/0/12907633/3563566_orig.jpg

V. Thapsus attracts generalized pollenates. Pictured below are small beetles and a honey bee pollenating the mullein flowers. The flower gives nectar and pollen as a reward for pollination. These flowers tend to grow abundantly in prairies and meadows so the changes of the generalized pollinator finding another mullein plant is likely.

http://cityjungle.files.wordpress.com/2013/07/img_1206.jpg?w=440&h=300&crop=1

https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhRRJk2uYCH5dD5Co6zqOlscafDlKzYGTu3BzJmc-cS2ea66L7CyCyPSDLb99QAWXecGWUTgR4fXBxot7v0fQX67oC2ZKrv_L9eAM188l-z9APjVvWzRIjuezEnndSKDZaJkoX6NMQD9S4P/s1600/Great+Mullein+04.jpg

I also found on a highly biased and unreliable site, herbcraft.org, the flower oil from mullein can treat ear infections, remove excess wax from ears, clean infected piercings, treat ear mites in animals, used as an antiseptic, can stop swelling when combined with garlic oil, and when ground ivy is added to it the combo can cure Meniere's disease..  

Growth

V. Thapsus is a biennial. The plant grows its leaves out wide and the roots thick and deep the first year. The second year the plant uses the stored energy from the previous year to grow tall and produce flowers and thereby seeds.

The plant has no secondary growth.
There are no growth rings because the leaves (Which makes up the entirety of the above ground portion of the plant) die with the frost, and is completely regrown each spring. That is why the plant stores it's provision of energy where the frost cannot steal it - in the roots. No newly grown foliage lasts to the next year.

Because of this growth pattern and looking at the picture I posted on the last blog, that the plant has a basal meristem that exists just below/at ground level that produces the next years foliage.

First year growth:

https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiGZ2-MYwRQU1xEAw-kqGV43CJx83jvIuclnQ1GUMDYlCe9YMyXL-JH_ecRA-lJFqG-P0dlC9lfUOBI7ENVAc_GTgZgWVzXOB_AQDAlm-2b_fl79Pf6hw3gUa3QIAXvBzf7irSHVOvPGPw/s1600/mullein+1.JPG

Second year growth:


http://www.ifa.hawaii.edu/info/vis/uploads/images/flora_fauna/mullein.jpg

I could not find any information on secondary growth in the roots, or if the roots die after the two years.