They're small now, but these stocks could grow much larger.California's giant redwood trees were once tiny sprouts or seeds. Likewise, the world's biggest companies were once much smaller. Trees and companies can grow significantly over time -- at least some of them.Three Motley Fool contributors think they've found biotech stocks that have the potential to become much larger. Here's why they think CRISPR Therapeutics (CRSP -2.94%), Zealand Pharma (ZLDP.F 0.89%), and Viking Therapeutics (VKTX 1.60%) are mon ...