Update file crossing_plants.md

assays/complementation_crosses/protocols/crossing_plants.md

-**crossing of plants**
+## Crossing of plants
 
+**Growth:**
 - grow parent plants in LD conditions
 - if parental plants have very different flowering times: sow the faster one with a bit of delay)
 
-
+**Crossing:**
 - emasculate florets from mother plants before pollen are shed (about Waddington stage 8.5 - 9.0)
 - pollinate florets with pollen from father plants, pollinate all florets from one spike with the same father: this is one cross
 - cover the spike with a paper bag, count later how many of the pollinated florets develop into seeds