Practical Botany – The Maltese Cross

 

Karen McMahon

Tested Studies in Laboratory Teaching, 2004, Volume 25

Abstract

One of the simplest tests to identify particles as starch is to view their appearance in polarizing light. Polarizing filters for student microscopes were made from inexpensive, long-lasting polarizing film. With their high degree of internal organization and relatively round shape, starch grains are almost crystalline in structure and exhibit birefringence under cross-polarized light. The starch grains appear bright against the dark field and each starch grain shows a Maltese cross when viewed with the light microscope. The presence of the telltale Maltese cross can be used to determine if starch is present and has many practical applications. In this laboratory exercise, students examine the properties of polarizing light and look for the presence of the distinctive Maltese cross in a variety of known and unknown substances to determine if starch is present.

Keywords:  starch

University of Nevada, Las Vegas (2003)