Needle-like crystals observed in wild-grape wine under microscope. Potentially harmful?
you are correct that these grapes have raphides. After doing some research, I found out that the grape raphides are twinned crystals. Raphides can cause much irritation for many herbivores (therefore, it is a protection mechanism) but less so for humans. In grapes, however, the irritation is much less than other raphide-containing species. This probably has to do eith the fact that it has a twinned structure (this is what I think, but I haven't found any research on this).

As a side note, what you have done is known as a whole mount, in which is entire organism specimen is placed on the slide, usually after crushing. It is a geeat way to examine the contents of the cell vacuole, which is where this raphides are commonly found.

References:


http://www.ncbi.nlm.nih.gov/pubmed/10648203
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0091341