Keith Murphy of H.A. Ponics posted this in one of the mail groups I belong to:
The First Guide from the British, That explains the Nutrient missing with picture
http://www.hbci.com/~wenonah/min-def/list.htm
The second is on Plant Physiology with pictures
http://4e.plantphys.net/article.php?ch=t&id=289
Check it out & bookmark it.