I don´t think the word morphotinctorial exists in English: very few Google hits and nearly all of them from Brazilian, Argentinian or Russian documents.

Morfo=shape, tintorial=que serve para tingir.

http://tinyurl.com/kvmlzr

Gram staining (or Gram's method) is an empirical method of differentiating bacterial species into two large groups (Gram-positive and Gram-negative) based on the chemical and physical properties of their cell walls.[1]
http://en.wikipedia.org/wiki/Gram_staining

chemical = staining; physical = shape.


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Note added at 27 mins (2009-08-26 15:51:34 GMT)
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Introduction
Morphology and staining characteristics of bacteria are essential to their identification. The Gram stain is one of the most valuable tools in clinical bacteriology, permitting the separation of bacteria into broadly related groups based on shape, size, and staining reaction. This method is a basic step in the classification of bacteria, i.e. a separation into Gram positive (G+) and Gram negative (G-) organisms.
http://www.lfhk.cuni.cz/klinmikrob/en/st_methods.htm