The cell theory was constructed by

robert hook

schleiden and schwann

carolus linnaeus

The cell theory was constructed by Schleiden and Schwann.

>Matthias Jakob Schleiden  was a German botanist and co-founder of the cell theory, along with Theodor Schwann and Rudolf Virchow (not really credited towards it, he is a contributor to the said theory.
>Robert Hook---largely attributed the cell theory;started the study of cells known as the cell biology.
>Carolus Linnaeus---a Swedish botanist, physician, and zoologist, who formalized the modern system of naming organisms called binomial nomenclature.

The answer would be sand and gravel