Herculis

[spenser]

19a describes the clockwise growth pattern of some climbing plants (11) -i-i-t-o---

12d an expert who is capable of appreciating the nuances of a field or subject (11) -o-n-----t-

5d metallic photoresistive elements used in components that measure light levels (8) -e-e-t-m

[hobbitess]

Areyou sure the penultimate letter is correct?

could the answer be connoisseur?

[kev100]

19a sinistrorse

[spenser]

I have catheter as the answer to ' long flexible tube used to introduce fluids to the body or to permit their withdrawal'. That is what gave me the t near the end of 12d.  I can't think of an alternative.

[alzheimer]

12d  How about cognoscente?

[spenser]

Aha cognoscente is what it is! Thanks everyone.

(though still stumped by 5d)

[brisyd]

5d  selenium

[alzheimer]

5d  How about selenium?   It kinda fits with the 14a= megalomania...I think    Any help?