Sorting tissues into their systems

Every tissue of the plant body belongs to one of the three tissue systems. You will finish a lookup table, write a function that uses it, and sort a list of tissues from a slide.

The idea. A dictionary can hold the lookup. Each tissue is a key of the dictionary, and its tissue system is the value.

Your tasks.

1. Add three entries to system_of: "trichome" for "epidermal", "medullary ray" for "ground", and "phloem" for "vascular".
2. In system_name, return the system for a tissue, or "unknown" if the tissue is not in the table.
3. Set vascular to a list of the names from slide that belong to the vascular system, in the order of slide.